Without delay, let's solve this. We've got 648 and we will be multiplying it by 420, that is, adding 648 to itself 420 times.
Step 1: 0 + 648 = 648
Step 2: 648 + 648 = 1296
Step 3: 1296 + 648 = 1944
Step 4: 1944 + 648 = 2592
Step 5: 2592 + 648 = 3240
Step 6: 3240 + 648 = 3888
Step 7: 3888 + 648 = 4536
Step 8: 4536 + 648 = 5184
Step 9: 5184 + 648 = 5832
Step 10: 5832 + 648 = 6480
Step 11: 6480 + 648 = 7128
Step 12: 7128 + 648 = 7776
Step 13: 7776 + 648 = 8424
Step 14: 8424 + 648 = 9072
Step 15: 9072 + 648 = 9720
Step 16: 9720 + 648 = 10368
Step 17: 10368 + 648 = 11016
Step 18: 11016 + 648 = 11664
Step 19: 11664 + 648 = 12312
Step 20: 12312 + 648 = 12960
Step 21: 12960 + 648 = 13608
Step 22: 13608 + 648 = 14256
Step 23: 14256 + 648 = 14904
Step 24: 14904 + 648 = 15552
Step 25: 15552 + 648 = 16200
Step 26: 16200 + 648 = 16848
Step 27: 16848 + 648 = 17496
Step 28: 17496 + 648 = 18144
Step 29: 18144 + 648 = 18792
Step 30: 18792 + 648 = 19440
Step 31: 19440 + 648 = 20088
Step 32: 20088 + 648 = 20736
Step 33: 20736 + 648 = 21384
Step 34: 21384 + 648 = 22032
Step 35: 22032 + 648 = 22680
Step 36: 22680 + 648 = 23328
Step 37: 23328 + 648 = 23976
Step 38: 23976 + 648 = 24624
Step 39: 24624 + 648 = 25272
Step 40: 25272 + 648 = 25920
Step 41: 25920 + 648 = 26568
Step 42: 26568 + 648 = 27216
Step 43: 27216 + 648 = 27864
Step 44: 27864 + 648 = 28512
Step 45: 28512 + 648 = 29160
Step 46: 29160 + 648 = 29808
Step 47: 29808 + 648 = 30456
Step 48: 30456 + 648 = 31104
Step 49: 31104 + 648 = 31752
Step 50: 31752 + 648 = 32400
Step 51: 32400 + 648 = 33048
Step 52: 33048 + 648 = 33696
Step 53: 33696 + 648 = 34344
Step 54: 34344 + 648 = 34992
Step 55: 34992 + 648 = 35640
Step 56: 35640 + 648 = 36288
Step 57: 36288 + 648 = 36936
Step 58: 36936 + 648 = 37584
Step 59: 37584 + 648 = 38232
Step 60: 38232 + 648 = 38880
Step 61: 38880 + 648 = 39528
Step 62: 39528 + 648 = 40176
Step 63: 40176 + 648 = 40824
Step 64: 40824 + 648 = 41472
Step 65: 41472 + 648 = 42120
Step 66: 42120 + 648 = 42768
Step 67: 42768 + 648 = 43416
Step 68: 43416 + 648 = 44064
Step 69: 44064 + 648 = 44712
Step 70: 44712 + 648 = 45360
Step 71: 45360 + 648 = 46008
Step 72: 46008 + 648 = 46656
Step 73: 46656 + 648 = 47304
Step 74: 47304 + 648 = 47952
Step 75: 47952 + 648 = 48600
Step 76: 48600 + 648 = 49248
Step 77: 49248 + 648 = 49896
Step 78: 49896 + 648 = 50544
Step 79: 50544 + 648 = 51192
Step 80: 51192 + 648 = 51840
Step 81: 51840 + 648 = 52488
Step 82: 52488 + 648 = 53136
Step 83: 53136 + 648 = 53784
Step 84: 53784 + 648 = 54432
Step 85: 54432 + 648 = 55080
Step 86: 55080 + 648 = 55728
Step 87: 55728 + 648 = 56376
Step 88: 56376 + 648 = 57024
Step 89: 57024 + 648 = 57672
Step 90: 57672 + 648 = 58320
Step 91: 58320 + 648 = 58968
Step 92: 58968 + 648 = 59616
Step 93: 59616 + 648 = 60264
Step 94: 60264 + 648 = 60912
Step 95: 60912 + 648 = 61560
Step 96: 61560 + 648 = 62208
Step 97: 62208 + 648 = 62856
Step 98: 62856 + 648 = 63504
Step 99: 63504 + 648 = 64152
Step 100: 64152 + 648 = 64800
Step 101: 64800 + 648 = 65448
Step 102: 65448 + 648 = 66096
Step 103: 66096 + 648 = 66744
Step 104: 66744 + 648 = 67392
Step 105: 67392 + 648 = 68040
Step 106: 68040 + 648 = 68688
Step 107: 68688 + 648 = 69336
Step 108: 69336 + 648 = 69984
Step 109: 69984 + 648 = 70632
Step 110: 70632 + 648 = 71280
Step 111: 71280 + 648 = 71928
Step 112: 71928 + 648 = 72576
Step 113: 72576 + 648 = 73224
Step 114: 73224 + 648 = 73872
Step 115: 73872 + 648 = 74520
Step 116: 74520 + 648 = 75168
Step 117: 75168 + 648 = 75816
Step 118: 75816 + 648 = 76464
Step 119: 76464 + 648 = 77112
Step 120: 77112 + 648 = 77760
Step 121: 77760 + 648 = 78408
Step 122: 78408 + 648 = 79056
Step 123: 79056 + 648 = 79704
Step 124: 79704 + 648 = 80352
Step 125: 80352 + 648 = 81000
Step 126: 81000 + 648 = 81648
Step 127: 81648 + 648 = 82296
Step 128: 82296 + 648 = 82944
Step 129: 82944 + 648 = 83592
Step 130: 83592 + 648 = 84240
Step 131: 84240 + 648 = 84888
Step 132: 84888 + 648 = 85536
Step 133: 85536 + 648 = 86184
Step 134: 86184 + 648 = 86832
Step 135: 86832 + 648 = 87480
Step 136: 87480 + 648 = 88128
Step 137: 88128 + 648 = 88776
Step 138: 88776 + 648 = 89424
Step 139: 89424 + 648 = 90072
Step 140: 90072 + 648 = 90720
Step 141: 90720 + 648 = 91368
Step 142: 91368 + 648 = 92016
Step 143: 92016 + 648 = 92664
Step 144: 92664 + 648 = 93312
Step 145: 93312 + 648 = 93960
Step 146: 93960 + 648 = 94608
Step 147: 94608 + 648 = 95256
Step 148: 95256 + 648 = 95904
Step 149: 95904 + 648 = 96552
Step 150: 96552 + 648 = 97200
Step 151: 97200 + 648 = 97848
Step 152: 97848 + 648 = 98496
Step 153: 98496 + 648 = 99144
Step 154: 99144 + 648 = 99792
Step 155: 99792 + 648 = 100440
Step 156: 100440 + 648 = 101088
Step 157: 101088 + 648 = 101736
Step 158: 101736 + 648 = 102384
Step 159: 102384 + 648 = 103032
Step 160: 103032 + 648 = 103680
Step 161: 103680 + 648 = 104328
Step 162: 104328 + 648 = 104976
Step 163: 104976 + 648 = 105624
Step 164: 105624 + 648 = 106272
Step 165: 106272 + 648 = 106920
Step 166: 106920 + 648 = 107568
Step 167: 107568 + 648 = 108216
Step 168: 108216 + 648 = 108864
Step 169: 108864 + 648 = 109512
Step 170: 109512 + 648 = 110160
Step 171: 110160 + 648 = 110808
Step 172: 110808 + 648 = 111456
Step 173: 111456 + 648 = 112104
Step 174: 112104 + 648 = 112752
Step 175: 112752 + 648 = 113400
Step 176: 113400 + 648 = 114048
Step 177: 114048 + 648 = 114696
Step 178: 114696 + 648 = 115344
Step 179: 115344 + 648 = 115992
Step 180: 115992 + 648 = 116640
Step 181: 116640 + 648 = 117288
Step 182: 117288 + 648 = 117936
Step 183: 117936 + 648 = 118584
Step 184: 118584 + 648 = 119232
Step 185: 119232 + 648 = 119880
Step 186: 119880 + 648 = 120528
Step 187: 120528 + 648 = 121176
Step 188: 121176 + 648 = 121824
Step 189: 121824 + 648 = 122472
Step 190: 122472 + 648 = 123120
Step 191: 123120 + 648 = 123768
Step 192: 123768 + 648 = 124416
Step 193: 124416 + 648 = 125064
Step 194: 125064 + 648 = 125712
Step 195: 125712 + 648 = 126360
Step 196: 126360 + 648 = 127008
Step 197: 127008 + 648 = 127656
Step 198: 127656 + 648 = 128304
Step 199: 128304 + 648 = 128952
Step 200: 128952 + 648 = 129600
Step 201: 129600 + 648 = 130248
Step 202: 130248 + 648 = 130896
Step 203: 130896 + 648 = 131544
Step 204: 131544 + 648 = 132192
Step 205: 132192 + 648 = 132840
Step 206: 132840 + 648 = 133488
Step 207: 133488 + 648 = 134136
Step 208: 134136 + 648 = 134784
Step 209: 134784 + 648 = 135432
Step 210: 135432 + 648 = 136080
Step 211: 136080 + 648 = 136728
Step 212: 136728 + 648 = 137376
Step 213: 137376 + 648 = 138024
Step 214: 138024 + 648 = 138672
Step 215: 138672 + 648 = 139320
Step 216: 139320 + 648 = 139968
Step 217: 139968 + 648 = 140616
Step 218: 140616 + 648 = 141264
Step 219: 141264 + 648 = 141912
Step 220: 141912 + 648 = 142560
Step 221: 142560 + 648 = 143208
Step 222: 143208 + 648 = 143856
Step 223: 143856 + 648 = 144504
Step 224: 144504 + 648 = 145152
Step 225: 145152 + 648 = 145800
Step 226: 145800 + 648 = 146448
Step 227: 146448 + 648 = 147096
Step 228: 147096 + 648 = 147744
Step 229: 147744 + 648 = 148392
Step 230: 148392 + 648 = 149040
Step 231: 149040 + 648 = 149688
Step 232: 149688 + 648 = 150336
Step 233: 150336 + 648 = 150984
Step 234: 150984 + 648 = 151632
Step 235: 151632 + 648 = 152280
Step 236: 152280 + 648 = 152928
Step 237: 152928 + 648 = 153576
Step 238: 153576 + 648 = 154224
Step 239: 154224 + 648 = 154872
Step 240: 154872 + 648 = 155520
Step 241: 155520 + 648 = 156168
Step 242: 156168 + 648 = 156816
Step 243: 156816 + 648 = 157464
Step 244: 157464 + 648 = 158112
Step 245: 158112 + 648 = 158760
Step 246: 158760 + 648 = 159408
Step 247: 159408 + 648 = 160056
Step 248: 160056 + 648 = 160704
Step 249: 160704 + 648 = 161352
Step 250: 161352 + 648 = 162000
Step 251: 162000 + 648 = 162648
Step 252: 162648 + 648 = 163296
Step 253: 163296 + 648 = 163944
Step 254: 163944 + 648 = 164592
Step 255: 164592 + 648 = 165240
Step 256: 165240 + 648 = 165888
Step 257: 165888 + 648 = 166536
Step 258: 166536 + 648 = 167184
Step 259: 167184 + 648 = 167832
Step 260: 167832 + 648 = 168480
Step 261: 168480 + 648 = 169128
Step 262: 169128 + 648 = 169776
Step 263: 169776 + 648 = 170424
Step 264: 170424 + 648 = 171072
Step 265: 171072 + 648 = 171720
Step 266: 171720 + 648 = 172368
Step 267: 172368 + 648 = 173016
Step 268: 173016 + 648 = 173664
Step 269: 173664 + 648 = 174312
Step 270: 174312 + 648 = 174960
Step 271: 174960 + 648 = 175608
Step 272: 175608 + 648 = 176256
Step 273: 176256 + 648 = 176904
Step 274: 176904 + 648 = 177552
Step 275: 177552 + 648 = 178200
Step 276: 178200 + 648 = 178848
Step 277: 178848 + 648 = 179496
Step 278: 179496 + 648 = 180144
Step 279: 180144 + 648 = 180792
Step 280: 180792 + 648 = 181440
Step 281: 181440 + 648 = 182088
Step 282: 182088 + 648 = 182736
Step 283: 182736 + 648 = 183384
Step 284: 183384 + 648 = 184032
Step 285: 184032 + 648 = 184680
Step 286: 184680 + 648 = 185328
Step 287: 185328 + 648 = 185976
Step 288: 185976 + 648 = 186624
Step 289: 186624 + 648 = 187272
Step 290: 187272 + 648 = 187920
Step 291: 187920 + 648 = 188568
Step 292: 188568 + 648 = 189216
Step 293: 189216 + 648 = 189864
Step 294: 189864 + 648 = 190512
Step 295: 190512 + 648 = 191160
Step 296: 191160 + 648 = 191808
Step 297: 191808 + 648 = 192456
Step 298: 192456 + 648 = 193104
Step 299: 193104 + 648 = 193752
Step 300: 193752 + 648 = 194400
Step 301: 194400 + 648 = 195048
Step 302: 195048 + 648 = 195696
Step 303: 195696 + 648 = 196344
Step 304: 196344 + 648 = 196992
Step 305: 196992 + 648 = 197640
Step 306: 197640 + 648 = 198288
Step 307: 198288 + 648 = 198936
Step 308: 198936 + 648 = 199584
Step 309: 199584 + 648 = 200232
Step 310: 200232 + 648 = 200880
Step 311: 200880 + 648 = 201528
Step 312: 201528 + 648 = 202176
Step 313: 202176 + 648 = 202824
Step 314: 202824 + 648 = 203472
Step 315: 203472 + 648 = 204120
Step 316: 204120 + 648 = 204768
Step 317: 204768 + 648 = 205416
Step 318: 205416 + 648 = 206064
Step 319: 206064 + 648 = 206712
Step 320: 206712 + 648 = 207360
Step 321: 207360 + 648 = 208008
Step 322: 208008 + 648 = 208656
Step 323: 208656 + 648 = 209304
Step 324: 209304 + 648 = 209952
Step 325: 209952 + 648 = 210600
Step 326: 210600 + 648 = 211248
Step 327: 211248 + 648 = 211896
Step 328: 211896 + 648 = 212544
Step 329: 212544 + 648 = 213192
Step 330: 213192 + 648 = 213840
Step 331: 213840 + 648 = 214488
Step 332: 214488 + 648 = 215136
Step 333: 215136 + 648 = 215784
Step 334: 215784 + 648 = 216432
Step 335: 216432 + 648 = 217080
Step 336: 217080 + 648 = 217728
Step 337: 217728 + 648 = 218376
Step 338: 218376 + 648 = 219024
Step 339: 219024 + 648 = 219672
Step 340: 219672 + 648 = 220320
Step 341: 220320 + 648 = 220968
Step 342: 220968 + 648 = 221616
Step 343: 221616 + 648 = 222264
Step 344: 222264 + 648 = 222912
Step 345: 222912 + 648 = 223560
Step 346: 223560 + 648 = 224208
Step 347: 224208 + 648 = 224856
Step 348: 224856 + 648 = 225504
Step 349: 225504 + 648 = 226152
Step 350: 226152 + 648 = 226800
Step 351: 226800 + 648 = 227448
Step 352: 227448 + 648 = 228096
Step 353: 228096 + 648 = 228744
Step 354: 228744 + 648 = 229392
Step 355: 229392 + 648 = 230040
Step 356: 230040 + 648 = 230688
Step 357: 230688 + 648 = 231336
Step 358: 231336 + 648 = 231984
Step 359: 231984 + 648 = 232632
Step 360: 232632 + 648 = 233280
Step 361: 233280 + 648 = 233928
Step 362: 233928 + 648 = 234576
Step 363: 234576 + 648 = 235224
Step 364: 235224 + 648 = 235872
Step 365: 235872 + 648 = 236520
Step 366: 236520 + 648 = 237168
Step 367: 237168 + 648 = 237816
Step 368: 237816 + 648 = 238464
Step 369: 238464 + 648 = 239112
Step 370: 239112 + 648 = 239760
Step 371: 239760 + 648 = 240408
Step 372: 240408 + 648 = 241056
Step 373: 241056 + 648 = 241704
Step 374: 241704 + 648 = 242352
Step 375: 242352 + 648 = 243000
Step 376: 243000 + 648 = 243648
Step 377: 243648 + 648 = 244296
Step 378: 244296 + 648 = 244944
Step 379: 244944 + 648 = 245592
Step 380: 245592 + 648 = 246240
Step 381: 246240 + 648 = 246888
Step 382: 246888 + 648 = 247536
Step 383: 247536 + 648 = 248184
Step 384: 248184 + 648 = 248832
Step 385: 248832 + 648 = 249480
Step 386: 249480 + 648 = 250128
Step 387: 250128 + 648 = 250776
Step 388: 250776 + 648 = 251424
Step 389: 251424 + 648 = 252072
Step 390: 252072 + 648 = 252720
Step 391: 252720 + 648 = 253368
Step 392: 253368 + 648 = 254016
Step 393: 254016 + 648 = 254664
Step 394: 254664 + 648 = 255312
Step 395: 255312 + 648 = 255960
Step 396: 255960 + 648 = 256608
Step 397: 256608 + 648 = 257256
Step 398: 257256 + 648 = 257904
Step 399: 257904 + 648 = 258552
Step 400: 258552 + 648 = 259200
Step 401: 259200 + 648 = 259848
Step 402: 259848 + 648 = 260496
Step 403: 260496 + 648 = 261144
Step 404: 261144 + 648 = 261792
Step 405: 261792 + 648 = 262440
Step 406: 262440 + 648 = 263088
Step 407: 263088 + 648 = 263736
Step 408: 263736 + 648 = 264384
Step 409: 264384 + 648 = 265032
Step 410: 265032 + 648 = 265680
Step 411: 265680 + 648 = 266328
Step 412: 266328 + 648 = 266976
Step 413: 266976 + 648 = 267624
Step 414: 267624 + 648 = 268272
Step 415: 268272 + 648 = 268920
Step 416: 268920 + 648 = 269568
Step 417: 269568 + 648 = 270216
Step 418: 270216 + 648 = 270864
Step 419: 270864 + 648 = 271512
Step 420: 271512 + 648 = 272160

So, 648*420 = 272160