OK, let's crack this. We're given 840 and our task is to multiply it by 317. Essentially, we'll be adding 840 to itself 317 times.
Step 1: 0 + 840 = 840
Step 2: 840 + 840 = 1680
Step 3: 1680 + 840 = 2520
Step 4: 2520 + 840 = 3360
Step 5: 3360 + 840 = 4200
Step 6: 4200 + 840 = 5040
Step 7: 5040 + 840 = 5880
Step 8: 5880 + 840 = 6720
Step 9: 6720 + 840 = 7560
Step 10: 7560 + 840 = 8400
Step 11: 8400 + 840 = 9240
Step 12: 9240 + 840 = 10080
Step 13: 10080 + 840 = 10920
Step 14: 10920 + 840 = 11760
Step 15: 11760 + 840 = 12600
Step 16: 12600 + 840 = 13440
Step 17: 13440 + 840 = 14280
Step 18: 14280 + 840 = 15120
Step 19: 15120 + 840 = 15960
Step 20: 15960 + 840 = 16800
Step 21: 16800 + 840 = 17640
Step 22: 17640 + 840 = 18480
Step 23: 18480 + 840 = 19320
Step 24: 19320 + 840 = 20160
Step 25: 20160 + 840 = 21000
Step 26: 21000 + 840 = 21840
Step 27: 21840 + 840 = 22680
Step 28: 22680 + 840 = 23520
Step 29: 23520 + 840 = 24360
Step 30: 24360 + 840 = 25200
Step 31: 25200 + 840 = 26040
Step 32: 26040 + 840 = 26880
Step 33: 26880 + 840 = 27720
Step 34: 27720 + 840 = 28560
Step 35: 28560 + 840 = 29400
Step 36: 29400 + 840 = 30240
Step 37: 30240 + 840 = 31080
Step 38: 31080 + 840 = 31920
Step 39: 31920 + 840 = 32760
Step 40: 32760 + 840 = 33600
Step 41: 33600 + 840 = 34440
Step 42: 34440 + 840 = 35280
Step 43: 35280 + 840 = 36120
Step 44: 36120 + 840 = 36960
Step 45: 36960 + 840 = 37800
Step 46: 37800 + 840 = 38640
Step 47: 38640 + 840 = 39480
Step 48: 39480 + 840 = 40320
Step 49: 40320 + 840 = 41160
Step 50: 41160 + 840 = 42000
Step 51: 42000 + 840 = 42840
Step 52: 42840 + 840 = 43680
Step 53: 43680 + 840 = 44520
Step 54: 44520 + 840 = 45360
Step 55: 45360 + 840 = 46200
Step 56: 46200 + 840 = 47040
Step 57: 47040 + 840 = 47880
Step 58: 47880 + 840 = 48720
Step 59: 48720 + 840 = 49560
Step 60: 49560 + 840 = 50400
Step 61: 50400 + 840 = 51240
Step 62: 51240 + 840 = 52080
Step 63: 52080 + 840 = 52920
Step 64: 52920 + 840 = 53760
Step 65: 53760 + 840 = 54600
Step 66: 54600 + 840 = 55440
Step 67: 55440 + 840 = 56280
Step 68: 56280 + 840 = 57120
Step 69: 57120 + 840 = 57960
Step 70: 57960 + 840 = 58800
Step 71: 58800 + 840 = 59640
Step 72: 59640 + 840 = 60480
Step 73: 60480 + 840 = 61320
Step 74: 61320 + 840 = 62160
Step 75: 62160 + 840 = 63000
Step 76: 63000 + 840 = 63840
Step 77: 63840 + 840 = 64680
Step 78: 64680 + 840 = 65520
Step 79: 65520 + 840 = 66360
Step 80: 66360 + 840 = 67200
Step 81: 67200 + 840 = 68040
Step 82: 68040 + 840 = 68880
Step 83: 68880 + 840 = 69720
Step 84: 69720 + 840 = 70560
Step 85: 70560 + 840 = 71400
Step 86: 71400 + 840 = 72240
Step 87: 72240 + 840 = 73080
Step 88: 73080 + 840 = 73920
Step 89: 73920 + 840 = 74760
Step 90: 74760 + 840 = 75600
Step 91: 75600 + 840 = 76440
Step 92: 76440 + 840 = 77280
Step 93: 77280 + 840 = 78120
Step 94: 78120 + 840 = 78960
Step 95: 78960 + 840 = 79800
Step 96: 79800 + 840 = 80640
Step 97: 80640 + 840 = 81480
Step 98: 81480 + 840 = 82320
Step 99: 82320 + 840 = 83160
Step 100: 83160 + 840 = 84000
Step 101: 84000 + 840 = 84840
Step 102: 84840 + 840 = 85680
Step 103: 85680 + 840 = 86520
Step 104: 86520 + 840 = 87360
Step 105: 87360 + 840 = 88200
Step 106: 88200 + 840 = 89040
Step 107: 89040 + 840 = 89880
Step 108: 89880 + 840 = 90720
Step 109: 90720 + 840 = 91560
Step 110: 91560 + 840 = 92400
Step 111: 92400 + 840 = 93240
Step 112: 93240 + 840 = 94080
Step 113: 94080 + 840 = 94920
Step 114: 94920 + 840 = 95760
Step 115: 95760 + 840 = 96600
Step 116: 96600 + 840 = 97440
Step 117: 97440 + 840 = 98280
Step 118: 98280 + 840 = 99120
Step 119: 99120 + 840 = 99960
Step 120: 99960 + 840 = 100800
Step 121: 100800 + 840 = 101640
Step 122: 101640 + 840 = 102480
Step 123: 102480 + 840 = 103320
Step 124: 103320 + 840 = 104160
Step 125: 104160 + 840 = 105000
Step 126: 105000 + 840 = 105840
Step 127: 105840 + 840 = 106680
Step 128: 106680 + 840 = 107520
Step 129: 107520 + 840 = 108360
Step 130: 108360 + 840 = 109200
Step 131: 109200 + 840 = 110040
Step 132: 110040 + 840 = 110880
Step 133: 110880 + 840 = 111720
Step 134: 111720 + 840 = 112560
Step 135: 112560 + 840 = 113400
Step 136: 113400 + 840 = 114240
Step 137: 114240 + 840 = 115080
Step 138: 115080 + 840 = 115920
Step 139: 115920 + 840 = 116760
Step 140: 116760 + 840 = 117600
Step 141: 117600 + 840 = 118440
Step 142: 118440 + 840 = 119280
Step 143: 119280 + 840 = 120120
Step 144: 120120 + 840 = 120960
Step 145: 120960 + 840 = 121800
Step 146: 121800 + 840 = 122640
Step 147: 122640 + 840 = 123480
Step 148: 123480 + 840 = 124320
Step 149: 124320 + 840 = 125160
Step 150: 125160 + 840 = 126000
Step 151: 126000 + 840 = 126840
Step 152: 126840 + 840 = 127680
Step 153: 127680 + 840 = 128520
Step 154: 128520 + 840 = 129360
Step 155: 129360 + 840 = 130200
Step 156: 130200 + 840 = 131040
Step 157: 131040 + 840 = 131880
Step 158: 131880 + 840 = 132720
Step 159: 132720 + 840 = 133560
Step 160: 133560 + 840 = 134400
Step 161: 134400 + 840 = 135240
Step 162: 135240 + 840 = 136080
Step 163: 136080 + 840 = 136920
Step 164: 136920 + 840 = 137760
Step 165: 137760 + 840 = 138600
Step 166: 138600 + 840 = 139440
Step 167: 139440 + 840 = 140280
Step 168: 140280 + 840 = 141120
Step 169: 141120 + 840 = 141960
Step 170: 141960 + 840 = 142800
Step 171: 142800 + 840 = 143640
Step 172: 143640 + 840 = 144480
Step 173: 144480 + 840 = 145320
Step 174: 145320 + 840 = 146160
Step 175: 146160 + 840 = 147000
Step 176: 147000 + 840 = 147840
Step 177: 147840 + 840 = 148680
Step 178: 148680 + 840 = 149520
Step 179: 149520 + 840 = 150360
Step 180: 150360 + 840 = 151200
Step 181: 151200 + 840 = 152040
Step 182: 152040 + 840 = 152880
Step 183: 152880 + 840 = 153720
Step 184: 153720 + 840 = 154560
Step 185: 154560 + 840 = 155400
Step 186: 155400 + 840 = 156240
Step 187: 156240 + 840 = 157080
Step 188: 157080 + 840 = 157920
Step 189: 157920 + 840 = 158760
Step 190: 158760 + 840 = 159600
Step 191: 159600 + 840 = 160440
Step 192: 160440 + 840 = 161280
Step 193: 161280 + 840 = 162120
Step 194: 162120 + 840 = 162960
Step 195: 162960 + 840 = 163800
Step 196: 163800 + 840 = 164640
Step 197: 164640 + 840 = 165480
Step 198: 165480 + 840 = 166320
Step 199: 166320 + 840 = 167160
Step 200: 167160 + 840 = 168000
Step 201: 168000 + 840 = 168840
Step 202: 168840 + 840 = 169680
Step 203: 169680 + 840 = 170520
Step 204: 170520 + 840 = 171360
Step 205: 171360 + 840 = 172200
Step 206: 172200 + 840 = 173040
Step 207: 173040 + 840 = 173880
Step 208: 173880 + 840 = 174720
Step 209: 174720 + 840 = 175560
Step 210: 175560 + 840 = 176400
Step 211: 176400 + 840 = 177240
Step 212: 177240 + 840 = 178080
Step 213: 178080 + 840 = 178920
Step 214: 178920 + 840 = 179760
Step 215: 179760 + 840 = 180600
Step 216: 180600 + 840 = 181440
Step 217: 181440 + 840 = 182280
Step 218: 182280 + 840 = 183120
Step 219: 183120 + 840 = 183960
Step 220: 183960 + 840 = 184800
Step 221: 184800 + 840 = 185640
Step 222: 185640 + 840 = 186480
Step 223: 186480 + 840 = 187320
Step 224: 187320 + 840 = 188160
Step 225: 188160 + 840 = 189000
Step 226: 189000 + 840 = 189840
Step 227: 189840 + 840 = 190680
Step 228: 190680 + 840 = 191520
Step 229: 191520 + 840 = 192360
Step 230: 192360 + 840 = 193200
Step 231: 193200 + 840 = 194040
Step 232: 194040 + 840 = 194880
Step 233: 194880 + 840 = 195720
Step 234: 195720 + 840 = 196560
Step 235: 196560 + 840 = 197400
Step 236: 197400 + 840 = 198240
Step 237: 198240 + 840 = 199080
Step 238: 199080 + 840 = 199920
Step 239: 199920 + 840 = 200760
Step 240: 200760 + 840 = 201600
Step 241: 201600 + 840 = 202440
Step 242: 202440 + 840 = 203280
Step 243: 203280 + 840 = 204120
Step 244: 204120 + 840 = 204960
Step 245: 204960 + 840 = 205800
Step 246: 205800 + 840 = 206640
Step 247: 206640 + 840 = 207480
Step 248: 207480 + 840 = 208320
Step 249: 208320 + 840 = 209160
Step 250: 209160 + 840 = 210000
Step 251: 210000 + 840 = 210840
Step 252: 210840 + 840 = 211680
Step 253: 211680 + 840 = 212520
Step 254: 212520 + 840 = 213360
Step 255: 213360 + 840 = 214200
Step 256: 214200 + 840 = 215040
Step 257: 215040 + 840 = 215880
Step 258: 215880 + 840 = 216720
Step 259: 216720 + 840 = 217560
Step 260: 217560 + 840 = 218400
Step 261: 218400 + 840 = 219240
Step 262: 219240 + 840 = 220080
Step 263: 220080 + 840 = 220920
Step 264: 220920 + 840 = 221760
Step 265: 221760 + 840 = 222600
Step 266: 222600 + 840 = 223440
Step 267: 223440 + 840 = 224280
Step 268: 224280 + 840 = 225120
Step 269: 225120 + 840 = 225960
Step 270: 225960 + 840 = 226800
Step 271: 226800 + 840 = 227640
Step 272: 227640 + 840 = 228480
Step 273: 228480 + 840 = 229320
Step 274: 229320 + 840 = 230160
Step 275: 230160 + 840 = 231000
Step 276: 231000 + 840 = 231840
Step 277: 231840 + 840 = 232680
Step 278: 232680 + 840 = 233520
Step 279: 233520 + 840 = 234360
Step 280: 234360 + 840 = 235200
Step 281: 235200 + 840 = 236040
Step 282: 236040 + 840 = 236880
Step 283: 236880 + 840 = 237720
Step 284: 237720 + 840 = 238560
Step 285: 238560 + 840 = 239400
Step 286: 239400 + 840 = 240240
Step 287: 240240 + 840 = 241080
Step 288: 241080 + 840 = 241920
Step 289: 241920 + 840 = 242760
Step 290: 242760 + 840 = 243600
Step 291: 243600 + 840 = 244440
Step 292: 244440 + 840 = 245280
Step 293: 245280 + 840 = 246120
Step 294: 246120 + 840 = 246960
Step 295: 246960 + 840 = 247800
Step 296: 247800 + 840 = 248640
Step 297: 248640 + 840 = 249480
Step 298: 249480 + 840 = 250320
Step 299: 250320 + 840 = 251160
Step 300: 251160 + 840 = 252000
Step 301: 252000 + 840 = 252840
Step 302: 252840 + 840 = 253680
Step 303: 253680 + 840 = 254520
Step 304: 254520 + 840 = 255360
Step 305: 255360 + 840 = 256200
Step 306: 256200 + 840 = 257040
Step 307: 257040 + 840 = 257880
Step 308: 257880 + 840 = 258720
Step 309: 258720 + 840 = 259560
Step 310: 259560 + 840 = 260400
Step 311: 260400 + 840 = 261240
Step 312: 261240 + 840 = 262080
Step 313: 262080 + 840 = 262920
Step 314: 262920 + 840 = 263760
Step 315: 263760 + 840 = 264600
Step 316: 264600 + 840 = 265440
Step 317: 265440 + 840 = 266280

So, 840*317 = 266280