Alright, let's solve this math problem step by step. First, we have the number 643. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 245. So, we're going to take the number 643 and add it to itself 245 times.
Step 1: 0 + 643 = 643
Step 2: 643 + 643 = 1286
Step 3: 1286 + 643 = 1929
Step 4: 1929 + 643 = 2572
Step 5: 2572 + 643 = 3215
Step 6: 3215 + 643 = 3858
Step 7: 3858 + 643 = 4501
Step 8: 4501 + 643 = 5144
Step 9: 5144 + 643 = 5787
Step 10: 5787 + 643 = 6430
Step 11: 6430 + 643 = 7073
Step 12: 7073 + 643 = 7716
Step 13: 7716 + 643 = 8359
Step 14: 8359 + 643 = 9002
Step 15: 9002 + 643 = 9645
Step 16: 9645 + 643 = 10288
Step 17: 10288 + 643 = 10931
Step 18: 10931 + 643 = 11574
Step 19: 11574 + 643 = 12217
Step 20: 12217 + 643 = 12860
Step 21: 12860 + 643 = 13503
Step 22: 13503 + 643 = 14146
Step 23: 14146 + 643 = 14789
Step 24: 14789 + 643 = 15432
Step 25: 15432 + 643 = 16075
Step 26: 16075 + 643 = 16718
Step 27: 16718 + 643 = 17361
Step 28: 17361 + 643 = 18004
Step 29: 18004 + 643 = 18647
Step 30: 18647 + 643 = 19290
Step 31: 19290 + 643 = 19933
Step 32: 19933 + 643 = 20576
Step 33: 20576 + 643 = 21219
Step 34: 21219 + 643 = 21862
Step 35: 21862 + 643 = 22505
Step 36: 22505 + 643 = 23148
Step 37: 23148 + 643 = 23791
Step 38: 23791 + 643 = 24434
Step 39: 24434 + 643 = 25077
Step 40: 25077 + 643 = 25720
Step 41: 25720 + 643 = 26363
Step 42: 26363 + 643 = 27006
Step 43: 27006 + 643 = 27649
Step 44: 27649 + 643 = 28292
Step 45: 28292 + 643 = 28935
Step 46: 28935 + 643 = 29578
Step 47: 29578 + 643 = 30221
Step 48: 30221 + 643 = 30864
Step 49: 30864 + 643 = 31507
Step 50: 31507 + 643 = 32150
Step 51: 32150 + 643 = 32793
Step 52: 32793 + 643 = 33436
Step 53: 33436 + 643 = 34079
Step 54: 34079 + 643 = 34722
Step 55: 34722 + 643 = 35365
Step 56: 35365 + 643 = 36008
Step 57: 36008 + 643 = 36651
Step 58: 36651 + 643 = 37294
Step 59: 37294 + 643 = 37937
Step 60: 37937 + 643 = 38580
Step 61: 38580 + 643 = 39223
Step 62: 39223 + 643 = 39866
Step 63: 39866 + 643 = 40509
Step 64: 40509 + 643 = 41152
Step 65: 41152 + 643 = 41795
Step 66: 41795 + 643 = 42438
Step 67: 42438 + 643 = 43081
Step 68: 43081 + 643 = 43724
Step 69: 43724 + 643 = 44367
Step 70: 44367 + 643 = 45010
Step 71: 45010 + 643 = 45653
Step 72: 45653 + 643 = 46296
Step 73: 46296 + 643 = 46939
Step 74: 46939 + 643 = 47582
Step 75: 47582 + 643 = 48225
Step 76: 48225 + 643 = 48868
Step 77: 48868 + 643 = 49511
Step 78: 49511 + 643 = 50154
Step 79: 50154 + 643 = 50797
Step 80: 50797 + 643 = 51440
Step 81: 51440 + 643 = 52083
Step 82: 52083 + 643 = 52726
Step 83: 52726 + 643 = 53369
Step 84: 53369 + 643 = 54012
Step 85: 54012 + 643 = 54655
Step 86: 54655 + 643 = 55298
Step 87: 55298 + 643 = 55941
Step 88: 55941 + 643 = 56584
Step 89: 56584 + 643 = 57227
Step 90: 57227 + 643 = 57870
Step 91: 57870 + 643 = 58513
Step 92: 58513 + 643 = 59156
Step 93: 59156 + 643 = 59799
Step 94: 59799 + 643 = 60442
Step 95: 60442 + 643 = 61085
Step 96: 61085 + 643 = 61728
Step 97: 61728 + 643 = 62371
Step 98: 62371 + 643 = 63014
Step 99: 63014 + 643 = 63657
Step 100: 63657 + 643 = 64300
Step 101: 64300 + 643 = 64943
Step 102: 64943 + 643 = 65586
Step 103: 65586 + 643 = 66229
Step 104: 66229 + 643 = 66872
Step 105: 66872 + 643 = 67515
Step 106: 67515 + 643 = 68158
Step 107: 68158 + 643 = 68801
Step 108: 68801 + 643 = 69444
Step 109: 69444 + 643 = 70087
Step 110: 70087 + 643 = 70730
Step 111: 70730 + 643 = 71373
Step 112: 71373 + 643 = 72016
Step 113: 72016 + 643 = 72659
Step 114: 72659 + 643 = 73302
Step 115: 73302 + 643 = 73945
Step 116: 73945 + 643 = 74588
Step 117: 74588 + 643 = 75231
Step 118: 75231 + 643 = 75874
Step 119: 75874 + 643 = 76517
Step 120: 76517 + 643 = 77160
Step 121: 77160 + 643 = 77803
Step 122: 77803 + 643 = 78446
Step 123: 78446 + 643 = 79089
Step 124: 79089 + 643 = 79732
Step 125: 79732 + 643 = 80375
Step 126: 80375 + 643 = 81018
Step 127: 81018 + 643 = 81661
Step 128: 81661 + 643 = 82304
Step 129: 82304 + 643 = 82947
Step 130: 82947 + 643 = 83590
Step 131: 83590 + 643 = 84233
Step 132: 84233 + 643 = 84876
Step 133: 84876 + 643 = 85519
Step 134: 85519 + 643 = 86162
Step 135: 86162 + 643 = 86805
Step 136: 86805 + 643 = 87448
Step 137: 87448 + 643 = 88091
Step 138: 88091 + 643 = 88734
Step 139: 88734 + 643 = 89377
Step 140: 89377 + 643 = 90020
Step 141: 90020 + 643 = 90663
Step 142: 90663 + 643 = 91306
Step 143: 91306 + 643 = 91949
Step 144: 91949 + 643 = 92592
Step 145: 92592 + 643 = 93235
Step 146: 93235 + 643 = 93878
Step 147: 93878 + 643 = 94521
Step 148: 94521 + 643 = 95164
Step 149: 95164 + 643 = 95807
Step 150: 95807 + 643 = 96450
Step 151: 96450 + 643 = 97093
Step 152: 97093 + 643 = 97736
Step 153: 97736 + 643 = 98379
Step 154: 98379 + 643 = 99022
Step 155: 99022 + 643 = 99665
Step 156: 99665 + 643 = 100308
Step 157: 100308 + 643 = 100951
Step 158: 100951 + 643 = 101594
Step 159: 101594 + 643 = 102237
Step 160: 102237 + 643 = 102880
Step 161: 102880 + 643 = 103523
Step 162: 103523 + 643 = 104166
Step 163: 104166 + 643 = 104809
Step 164: 104809 + 643 = 105452
Step 165: 105452 + 643 = 106095
Step 166: 106095 + 643 = 106738
Step 167: 106738 + 643 = 107381
Step 168: 107381 + 643 = 108024
Step 169: 108024 + 643 = 108667
Step 170: 108667 + 643 = 109310
Step 171: 109310 + 643 = 109953
Step 172: 109953 + 643 = 110596
Step 173: 110596 + 643 = 111239
Step 174: 111239 + 643 = 111882
Step 175: 111882 + 643 = 112525
Step 176: 112525 + 643 = 113168
Step 177: 113168 + 643 = 113811
Step 178: 113811 + 643 = 114454
Step 179: 114454 + 643 = 115097
Step 180: 115097 + 643 = 115740
Step 181: 115740 + 643 = 116383
Step 182: 116383 + 643 = 117026
Step 183: 117026 + 643 = 117669
Step 184: 117669 + 643 = 118312
Step 185: 118312 + 643 = 118955
Step 186: 118955 + 643 = 119598
Step 187: 119598 + 643 = 120241
Step 188: 120241 + 643 = 120884
Step 189: 120884 + 643 = 121527
Step 190: 121527 + 643 = 122170
Step 191: 122170 + 643 = 122813
Step 192: 122813 + 643 = 123456
Step 193: 123456 + 643 = 124099
Step 194: 124099 + 643 = 124742
Step 195: 124742 + 643 = 125385
Step 196: 125385 + 643 = 126028
Step 197: 126028 + 643 = 126671
Step 198: 126671 + 643 = 127314
Step 199: 127314 + 643 = 127957
Step 200: 127957 + 643 = 128600
Step 201: 128600 + 643 = 129243
Step 202: 129243 + 643 = 129886
Step 203: 129886 + 643 = 130529
Step 204: 130529 + 643 = 131172
Step 205: 131172 + 643 = 131815
Step 206: 131815 + 643 = 132458
Step 207: 132458 + 643 = 133101
Step 208: 133101 + 643 = 133744
Step 209: 133744 + 643 = 134387
Step 210: 134387 + 643 = 135030
Step 211: 135030 + 643 = 135673
Step 212: 135673 + 643 = 136316
Step 213: 136316 + 643 = 136959
Step 214: 136959 + 643 = 137602
Step 215: 137602 + 643 = 138245
Step 216: 138245 + 643 = 138888
Step 217: 138888 + 643 = 139531
Step 218: 139531 + 643 = 140174
Step 219: 140174 + 643 = 140817
Step 220: 140817 + 643 = 141460
Step 221: 141460 + 643 = 142103
Step 222: 142103 + 643 = 142746
Step 223: 142746 + 643 = 143389
Step 224: 143389 + 643 = 144032
Step 225: 144032 + 643 = 144675
Step 226: 144675 + 643 = 145318
Step 227: 145318 + 643 = 145961
Step 228: 145961 + 643 = 146604
Step 229: 146604 + 643 = 147247
Step 230: 147247 + 643 = 147890
Step 231: 147890 + 643 = 148533
Step 232: 148533 + 643 = 149176
Step 233: 149176 + 643 = 149819
Step 234: 149819 + 643 = 150462
Step 235: 150462 + 643 = 151105
Step 236: 151105 + 643 = 151748
Step 237: 151748 + 643 = 152391
Step 238: 152391 + 643 = 153034
Step 239: 153034 + 643 = 153677
Step 240: 153677 + 643 = 154320
Step 241: 154320 + 643 = 154963
Step 242: 154963 + 643 = 155606
Step 243: 155606 + 643 = 156249
Step 244: 156249 + 643 = 156892
Step 245: 156892 + 643 = 157535

So, 643*245 = 157535