OK, let's work through this together. We're starting with 638 and we're going to multiply it by 143, which means we add 638 to itself 143 times.
Step 1: 0 + 638 = 638
Step 2: 638 + 638 = 1276
Step 3: 1276 + 638 = 1914
Step 4: 1914 + 638 = 2552
Step 5: 2552 + 638 = 3190
Step 6: 3190 + 638 = 3828
Step 7: 3828 + 638 = 4466
Step 8: 4466 + 638 = 5104
Step 9: 5104 + 638 = 5742
Step 10: 5742 + 638 = 6380
Step 11: 6380 + 638 = 7018
Step 12: 7018 + 638 = 7656
Step 13: 7656 + 638 = 8294
Step 14: 8294 + 638 = 8932
Step 15: 8932 + 638 = 9570
Step 16: 9570 + 638 = 10208
Step 17: 10208 + 638 = 10846
Step 18: 10846 + 638 = 11484
Step 19: 11484 + 638 = 12122
Step 20: 12122 + 638 = 12760
Step 21: 12760 + 638 = 13398
Step 22: 13398 + 638 = 14036
Step 23: 14036 + 638 = 14674
Step 24: 14674 + 638 = 15312
Step 25: 15312 + 638 = 15950
Step 26: 15950 + 638 = 16588
Step 27: 16588 + 638 = 17226
Step 28: 17226 + 638 = 17864
Step 29: 17864 + 638 = 18502
Step 30: 18502 + 638 = 19140
Step 31: 19140 + 638 = 19778
Step 32: 19778 + 638 = 20416
Step 33: 20416 + 638 = 21054
Step 34: 21054 + 638 = 21692
Step 35: 21692 + 638 = 22330
Step 36: 22330 + 638 = 22968
Step 37: 22968 + 638 = 23606
Step 38: 23606 + 638 = 24244
Step 39: 24244 + 638 = 24882
Step 40: 24882 + 638 = 25520
Step 41: 25520 + 638 = 26158
Step 42: 26158 + 638 = 26796
Step 43: 26796 + 638 = 27434
Step 44: 27434 + 638 = 28072
Step 45: 28072 + 638 = 28710
Step 46: 28710 + 638 = 29348
Step 47: 29348 + 638 = 29986
Step 48: 29986 + 638 = 30624
Step 49: 30624 + 638 = 31262
Step 50: 31262 + 638 = 31900
Step 51: 31900 + 638 = 32538
Step 52: 32538 + 638 = 33176
Step 53: 33176 + 638 = 33814
Step 54: 33814 + 638 = 34452
Step 55: 34452 + 638 = 35090
Step 56: 35090 + 638 = 35728
Step 57: 35728 + 638 = 36366
Step 58: 36366 + 638 = 37004
Step 59: 37004 + 638 = 37642
Step 60: 37642 + 638 = 38280
Step 61: 38280 + 638 = 38918
Step 62: 38918 + 638 = 39556
Step 63: 39556 + 638 = 40194
Step 64: 40194 + 638 = 40832
Step 65: 40832 + 638 = 41470
Step 66: 41470 + 638 = 42108
Step 67: 42108 + 638 = 42746
Step 68: 42746 + 638 = 43384
Step 69: 43384 + 638 = 44022
Step 70: 44022 + 638 = 44660
Step 71: 44660 + 638 = 45298
Step 72: 45298 + 638 = 45936
Step 73: 45936 + 638 = 46574
Step 74: 46574 + 638 = 47212
Step 75: 47212 + 638 = 47850
Step 76: 47850 + 638 = 48488
Step 77: 48488 + 638 = 49126
Step 78: 49126 + 638 = 49764
Step 79: 49764 + 638 = 50402
Step 80: 50402 + 638 = 51040
Step 81: 51040 + 638 = 51678
Step 82: 51678 + 638 = 52316
Step 83: 52316 + 638 = 52954
Step 84: 52954 + 638 = 53592
Step 85: 53592 + 638 = 54230
Step 86: 54230 + 638 = 54868
Step 87: 54868 + 638 = 55506
Step 88: 55506 + 638 = 56144
Step 89: 56144 + 638 = 56782
Step 90: 56782 + 638 = 57420
Step 91: 57420 + 638 = 58058
Step 92: 58058 + 638 = 58696
Step 93: 58696 + 638 = 59334
Step 94: 59334 + 638 = 59972
Step 95: 59972 + 638 = 60610
Step 96: 60610 + 638 = 61248
Step 97: 61248 + 638 = 61886
Step 98: 61886 + 638 = 62524
Step 99: 62524 + 638 = 63162
Step 100: 63162 + 638 = 63800
Step 101: 63800 + 638 = 64438
Step 102: 64438 + 638 = 65076
Step 103: 65076 + 638 = 65714
Step 104: 65714 + 638 = 66352
Step 105: 66352 + 638 = 66990
Step 106: 66990 + 638 = 67628
Step 107: 67628 + 638 = 68266
Step 108: 68266 + 638 = 68904
Step 109: 68904 + 638 = 69542
Step 110: 69542 + 638 = 70180
Step 111: 70180 + 638 = 70818
Step 112: 70818 + 638 = 71456
Step 113: 71456 + 638 = 72094
Step 114: 72094 + 638 = 72732
Step 115: 72732 + 638 = 73370
Step 116: 73370 + 638 = 74008
Step 117: 74008 + 638 = 74646
Step 118: 74646 + 638 = 75284
Step 119: 75284 + 638 = 75922
Step 120: 75922 + 638 = 76560
Step 121: 76560 + 638 = 77198
Step 122: 77198 + 638 = 77836
Step 123: 77836 + 638 = 78474
Step 124: 78474 + 638 = 79112
Step 125: 79112 + 638 = 79750
Step 126: 79750 + 638 = 80388
Step 127: 80388 + 638 = 81026
Step 128: 81026 + 638 = 81664
Step 129: 81664 + 638 = 82302
Step 130: 82302 + 638 = 82940
Step 131: 82940 + 638 = 83578
Step 132: 83578 + 638 = 84216
Step 133: 84216 + 638 = 84854
Step 134: 84854 + 638 = 85492
Step 135: 85492 + 638 = 86130
Step 136: 86130 + 638 = 86768
Step 137: 86768 + 638 = 87406
Step 138: 87406 + 638 = 88044
Step 139: 88044 + 638 = 88682
Step 140: 88682 + 638 = 89320
Step 141: 89320 + 638 = 89958
Step 142: 89958 + 638 = 90596
Step 143: 90596 + 638 = 91234

So, 638*143 = 91234