OK, let's work through this together. We're starting with 423 and we're going to multiply it by 159, which means we add 423 to itself 159 times.
Step 1: 0 + 423 = 423
Step 2: 423 + 423 = 846
Step 3: 846 + 423 = 1269
Step 4: 1269 + 423 = 1692
Step 5: 1692 + 423 = 2115
Step 6: 2115 + 423 = 2538
Step 7: 2538 + 423 = 2961
Step 8: 2961 + 423 = 3384
Step 9: 3384 + 423 = 3807
Step 10: 3807 + 423 = 4230
Step 11: 4230 + 423 = 4653
Step 12: 4653 + 423 = 5076
Step 13: 5076 + 423 = 5499
Step 14: 5499 + 423 = 5922
Step 15: 5922 + 423 = 6345
Step 16: 6345 + 423 = 6768
Step 17: 6768 + 423 = 7191
Step 18: 7191 + 423 = 7614
Step 19: 7614 + 423 = 8037
Step 20: 8037 + 423 = 8460
Step 21: 8460 + 423 = 8883
Step 22: 8883 + 423 = 9306
Step 23: 9306 + 423 = 9729
Step 24: 9729 + 423 = 10152
Step 25: 10152 + 423 = 10575
Step 26: 10575 + 423 = 10998
Step 27: 10998 + 423 = 11421
Step 28: 11421 + 423 = 11844
Step 29: 11844 + 423 = 12267
Step 30: 12267 + 423 = 12690
Step 31: 12690 + 423 = 13113
Step 32: 13113 + 423 = 13536
Step 33: 13536 + 423 = 13959
Step 34: 13959 + 423 = 14382
Step 35: 14382 + 423 = 14805
Step 36: 14805 + 423 = 15228
Step 37: 15228 + 423 = 15651
Step 38: 15651 + 423 = 16074
Step 39: 16074 + 423 = 16497
Step 40: 16497 + 423 = 16920
Step 41: 16920 + 423 = 17343
Step 42: 17343 + 423 = 17766
Step 43: 17766 + 423 = 18189
Step 44: 18189 + 423 = 18612
Step 45: 18612 + 423 = 19035
Step 46: 19035 + 423 = 19458
Step 47: 19458 + 423 = 19881
Step 48: 19881 + 423 = 20304
Step 49: 20304 + 423 = 20727
Step 50: 20727 + 423 = 21150
Step 51: 21150 + 423 = 21573
Step 52: 21573 + 423 = 21996
Step 53: 21996 + 423 = 22419
Step 54: 22419 + 423 = 22842
Step 55: 22842 + 423 = 23265
Step 56: 23265 + 423 = 23688
Step 57: 23688 + 423 = 24111
Step 58: 24111 + 423 = 24534
Step 59: 24534 + 423 = 24957
Step 60: 24957 + 423 = 25380
Step 61: 25380 + 423 = 25803
Step 62: 25803 + 423 = 26226
Step 63: 26226 + 423 = 26649
Step 64: 26649 + 423 = 27072
Step 65: 27072 + 423 = 27495
Step 66: 27495 + 423 = 27918
Step 67: 27918 + 423 = 28341
Step 68: 28341 + 423 = 28764
Step 69: 28764 + 423 = 29187
Step 70: 29187 + 423 = 29610
Step 71: 29610 + 423 = 30033
Step 72: 30033 + 423 = 30456
Step 73: 30456 + 423 = 30879
Step 74: 30879 + 423 = 31302
Step 75: 31302 + 423 = 31725
Step 76: 31725 + 423 = 32148
Step 77: 32148 + 423 = 32571
Step 78: 32571 + 423 = 32994
Step 79: 32994 + 423 = 33417
Step 80: 33417 + 423 = 33840
Step 81: 33840 + 423 = 34263
Step 82: 34263 + 423 = 34686
Step 83: 34686 + 423 = 35109
Step 84: 35109 + 423 = 35532
Step 85: 35532 + 423 = 35955
Step 86: 35955 + 423 = 36378
Step 87: 36378 + 423 = 36801
Step 88: 36801 + 423 = 37224
Step 89: 37224 + 423 = 37647
Step 90: 37647 + 423 = 38070
Step 91: 38070 + 423 = 38493
Step 92: 38493 + 423 = 38916
Step 93: 38916 + 423 = 39339
Step 94: 39339 + 423 = 39762
Step 95: 39762 + 423 = 40185
Step 96: 40185 + 423 = 40608
Step 97: 40608 + 423 = 41031
Step 98: 41031 + 423 = 41454
Step 99: 41454 + 423 = 41877
Step 100: 41877 + 423 = 42300
Step 101: 42300 + 423 = 42723
Step 102: 42723 + 423 = 43146
Step 103: 43146 + 423 = 43569
Step 104: 43569 + 423 = 43992
Step 105: 43992 + 423 = 44415
Step 106: 44415 + 423 = 44838
Step 107: 44838 + 423 = 45261
Step 108: 45261 + 423 = 45684
Step 109: 45684 + 423 = 46107
Step 110: 46107 + 423 = 46530
Step 111: 46530 + 423 = 46953
Step 112: 46953 + 423 = 47376
Step 113: 47376 + 423 = 47799
Step 114: 47799 + 423 = 48222
Step 115: 48222 + 423 = 48645
Step 116: 48645 + 423 = 49068
Step 117: 49068 + 423 = 49491
Step 118: 49491 + 423 = 49914
Step 119: 49914 + 423 = 50337
Step 120: 50337 + 423 = 50760
Step 121: 50760 + 423 = 51183
Step 122: 51183 + 423 = 51606
Step 123: 51606 + 423 = 52029
Step 124: 52029 + 423 = 52452
Step 125: 52452 + 423 = 52875
Step 126: 52875 + 423 = 53298
Step 127: 53298 + 423 = 53721
Step 128: 53721 + 423 = 54144
Step 129: 54144 + 423 = 54567
Step 130: 54567 + 423 = 54990
Step 131: 54990 + 423 = 55413
Step 132: 55413 + 423 = 55836
Step 133: 55836 + 423 = 56259
Step 134: 56259 + 423 = 56682
Step 135: 56682 + 423 = 57105
Step 136: 57105 + 423 = 57528
Step 137: 57528 + 423 = 57951
Step 138: 57951 + 423 = 58374
Step 139: 58374 + 423 = 58797
Step 140: 58797 + 423 = 59220
Step 141: 59220 + 423 = 59643
Step 142: 59643 + 423 = 60066
Step 143: 60066 + 423 = 60489
Step 144: 60489 + 423 = 60912
Step 145: 60912 + 423 = 61335
Step 146: 61335 + 423 = 61758
Step 147: 61758 + 423 = 62181
Step 148: 62181 + 423 = 62604
Step 149: 62604 + 423 = 63027
Step 150: 63027 + 423 = 63450
Step 151: 63450 + 423 = 63873
Step 152: 63873 + 423 = 64296
Step 153: 64296 + 423 = 64719
Step 154: 64719 + 423 = 65142
Step 155: 65142 + 423 = 65565
Step 156: 65565 + 423 = 65988
Step 157: 65988 + 423 = 66411
Step 158: 66411 + 423 = 66834
Step 159: 66834 + 423 = 67257

So, 423*159 = 67257