Sure thing! We've got 81 and we're gonna multiply it by 157. That's the same as adding 81 to itself 157 times.
Step 1: 0 + 81 = 81
Step 2: 81 + 81 = 162
Step 3: 162 + 81 = 243
Step 4: 243 + 81 = 324
Step 5: 324 + 81 = 405
Step 6: 405 + 81 = 486
Step 7: 486 + 81 = 567
Step 8: 567 + 81 = 648
Step 9: 648 + 81 = 729
Step 10: 729 + 81 = 810
Step 11: 810 + 81 = 891
Step 12: 891 + 81 = 972
Step 13: 972 + 81 = 1053
Step 14: 1053 + 81 = 1134
Step 15: 1134 + 81 = 1215
Step 16: 1215 + 81 = 1296
Step 17: 1296 + 81 = 1377
Step 18: 1377 + 81 = 1458
Step 19: 1458 + 81 = 1539
Step 20: 1539 + 81 = 1620
Step 21: 1620 + 81 = 1701
Step 22: 1701 + 81 = 1782
Step 23: 1782 + 81 = 1863
Step 24: 1863 + 81 = 1944
Step 25: 1944 + 81 = 2025
Step 26: 2025 + 81 = 2106
Step 27: 2106 + 81 = 2187
Step 28: 2187 + 81 = 2268
Step 29: 2268 + 81 = 2349
Step 30: 2349 + 81 = 2430
Step 31: 2430 + 81 = 2511
Step 32: 2511 + 81 = 2592
Step 33: 2592 + 81 = 2673
Step 34: 2673 + 81 = 2754
Step 35: 2754 + 81 = 2835
Step 36: 2835 + 81 = 2916
Step 37: 2916 + 81 = 2997
Step 38: 2997 + 81 = 3078
Step 39: 3078 + 81 = 3159
Step 40: 3159 + 81 = 3240
Step 41: 3240 + 81 = 3321
Step 42: 3321 + 81 = 3402
Step 43: 3402 + 81 = 3483
Step 44: 3483 + 81 = 3564
Step 45: 3564 + 81 = 3645
Step 46: 3645 + 81 = 3726
Step 47: 3726 + 81 = 3807
Step 48: 3807 + 81 = 3888
Step 49: 3888 + 81 = 3969
Step 50: 3969 + 81 = 4050
Step 51: 4050 + 81 = 4131
Step 52: 4131 + 81 = 4212
Step 53: 4212 + 81 = 4293
Step 54: 4293 + 81 = 4374
Step 55: 4374 + 81 = 4455
Step 56: 4455 + 81 = 4536
Step 57: 4536 + 81 = 4617
Step 58: 4617 + 81 = 4698
Step 59: 4698 + 81 = 4779
Step 60: 4779 + 81 = 4860
Step 61: 4860 + 81 = 4941
Step 62: 4941 + 81 = 5022
Step 63: 5022 + 81 = 5103
Step 64: 5103 + 81 = 5184
Step 65: 5184 + 81 = 5265
Step 66: 5265 + 81 = 5346
Step 67: 5346 + 81 = 5427
Step 68: 5427 + 81 = 5508
Step 69: 5508 + 81 = 5589
Step 70: 5589 + 81 = 5670
Step 71: 5670 + 81 = 5751
Step 72: 5751 + 81 = 5832
Step 73: 5832 + 81 = 5913
Step 74: 5913 + 81 = 5994
Step 75: 5994 + 81 = 6075
Step 76: 6075 + 81 = 6156
Step 77: 6156 + 81 = 6237
Step 78: 6237 + 81 = 6318
Step 79: 6318 + 81 = 6399
Step 80: 6399 + 81 = 6480
Step 81: 6480 + 81 = 6561
Step 82: 6561 + 81 = 6642
Step 83: 6642 + 81 = 6723
Step 84: 6723 + 81 = 6804
Step 85: 6804 + 81 = 6885
Step 86: 6885 + 81 = 6966
Step 87: 6966 + 81 = 7047
Step 88: 7047 + 81 = 7128
Step 89: 7128 + 81 = 7209
Step 90: 7209 + 81 = 7290
Step 91: 7290 + 81 = 7371
Step 92: 7371 + 81 = 7452
Step 93: 7452 + 81 = 7533
Step 94: 7533 + 81 = 7614
Step 95: 7614 + 81 = 7695
Step 96: 7695 + 81 = 7776
Step 97: 7776 + 81 = 7857
Step 98: 7857 + 81 = 7938
Step 99: 7938 + 81 = 8019
Step 100: 8019 + 81 = 8100
Step 101: 8100 + 81 = 8181
Step 102: 8181 + 81 = 8262
Step 103: 8262 + 81 = 8343
Step 104: 8343 + 81 = 8424
Step 105: 8424 + 81 = 8505
Step 106: 8505 + 81 = 8586
Step 107: 8586 + 81 = 8667
Step 108: 8667 + 81 = 8748
Step 109: 8748 + 81 = 8829
Step 110: 8829 + 81 = 8910
Step 111: 8910 + 81 = 8991
Step 112: 8991 + 81 = 9072
Step 113: 9072 + 81 = 9153
Step 114: 9153 + 81 = 9234
Step 115: 9234 + 81 = 9315
Step 116: 9315 + 81 = 9396
Step 117: 9396 + 81 = 9477
Step 118: 9477 + 81 = 9558
Step 119: 9558 + 81 = 9639
Step 120: 9639 + 81 = 9720
Step 121: 9720 + 81 = 9801
Step 122: 9801 + 81 = 9882
Step 123: 9882 + 81 = 9963
Step 124: 9963 + 81 = 10044
Step 125: 10044 + 81 = 10125
Step 126: 10125 + 81 = 10206
Step 127: 10206 + 81 = 10287
Step 128: 10287 + 81 = 10368
Step 129: 10368 + 81 = 10449
Step 130: 10449 + 81 = 10530
Step 131: 10530 + 81 = 10611
Step 132: 10611 + 81 = 10692
Step 133: 10692 + 81 = 10773
Step 134: 10773 + 81 = 10854
Step 135: 10854 + 81 = 10935
Step 136: 10935 + 81 = 11016
Step 137: 11016 + 81 = 11097
Step 138: 11097 + 81 = 11178
Step 139: 11178 + 81 = 11259
Step 140: 11259 + 81 = 11340
Step 141: 11340 + 81 = 11421
Step 142: 11421 + 81 = 11502
Step 143: 11502 + 81 = 11583
Step 144: 11583 + 81 = 11664
Step 145: 11664 + 81 = 11745
Step 146: 11745 + 81 = 11826
Step 147: 11826 + 81 = 11907
Step 148: 11907 + 81 = 11988
Step 149: 11988 + 81 = 12069
Step 150: 12069 + 81 = 12150
Step 151: 12150 + 81 = 12231
Step 152: 12231 + 81 = 12312
Step 153: 12312 + 81 = 12393
Step 154: 12393 + 81 = 12474
Step 155: 12474 + 81 = 12555
Step 156: 12555 + 81 = 12636
Step 157: 12636 + 81 = 12717

So, 81*157 = 12717