OK, let's work through this together. We're starting with 87 and we're going to multiply it by 142, which means we add 87 to itself 142 times.
Step 1: 0 + 87 = 87
Step 2: 87 + 87 = 174
Step 3: 174 + 87 = 261
Step 4: 261 + 87 = 348
Step 5: 348 + 87 = 435
Step 6: 435 + 87 = 522
Step 7: 522 + 87 = 609
Step 8: 609 + 87 = 696
Step 9: 696 + 87 = 783
Step 10: 783 + 87 = 870
Step 11: 870 + 87 = 957
Step 12: 957 + 87 = 1044
Step 13: 1044 + 87 = 1131
Step 14: 1131 + 87 = 1218
Step 15: 1218 + 87 = 1305
Step 16: 1305 + 87 = 1392
Step 17: 1392 + 87 = 1479
Step 18: 1479 + 87 = 1566
Step 19: 1566 + 87 = 1653
Step 20: 1653 + 87 = 1740
Step 21: 1740 + 87 = 1827
Step 22: 1827 + 87 = 1914
Step 23: 1914 + 87 = 2001
Step 24: 2001 + 87 = 2088
Step 25: 2088 + 87 = 2175
Step 26: 2175 + 87 = 2262
Step 27: 2262 + 87 = 2349
Step 28: 2349 + 87 = 2436
Step 29: 2436 + 87 = 2523
Step 30: 2523 + 87 = 2610
Step 31: 2610 + 87 = 2697
Step 32: 2697 + 87 = 2784
Step 33: 2784 + 87 = 2871
Step 34: 2871 + 87 = 2958
Step 35: 2958 + 87 = 3045
Step 36: 3045 + 87 = 3132
Step 37: 3132 + 87 = 3219
Step 38: 3219 + 87 = 3306
Step 39: 3306 + 87 = 3393
Step 40: 3393 + 87 = 3480
Step 41: 3480 + 87 = 3567
Step 42: 3567 + 87 = 3654
Step 43: 3654 + 87 = 3741
Step 44: 3741 + 87 = 3828
Step 45: 3828 + 87 = 3915
Step 46: 3915 + 87 = 4002
Step 47: 4002 + 87 = 4089
Step 48: 4089 + 87 = 4176
Step 49: 4176 + 87 = 4263
Step 50: 4263 + 87 = 4350
Step 51: 4350 + 87 = 4437
Step 52: 4437 + 87 = 4524
Step 53: 4524 + 87 = 4611
Step 54: 4611 + 87 = 4698
Step 55: 4698 + 87 = 4785
Step 56: 4785 + 87 = 4872
Step 57: 4872 + 87 = 4959
Step 58: 4959 + 87 = 5046
Step 59: 5046 + 87 = 5133
Step 60: 5133 + 87 = 5220
Step 61: 5220 + 87 = 5307
Step 62: 5307 + 87 = 5394
Step 63: 5394 + 87 = 5481
Step 64: 5481 + 87 = 5568
Step 65: 5568 + 87 = 5655
Step 66: 5655 + 87 = 5742
Step 67: 5742 + 87 = 5829
Step 68: 5829 + 87 = 5916
Step 69: 5916 + 87 = 6003
Step 70: 6003 + 87 = 6090
Step 71: 6090 + 87 = 6177
Step 72: 6177 + 87 = 6264
Step 73: 6264 + 87 = 6351
Step 74: 6351 + 87 = 6438
Step 75: 6438 + 87 = 6525
Step 76: 6525 + 87 = 6612
Step 77: 6612 + 87 = 6699
Step 78: 6699 + 87 = 6786
Step 79: 6786 + 87 = 6873
Step 80: 6873 + 87 = 6960
Step 81: 6960 + 87 = 7047
Step 82: 7047 + 87 = 7134
Step 83: 7134 + 87 = 7221
Step 84: 7221 + 87 = 7308
Step 85: 7308 + 87 = 7395
Step 86: 7395 + 87 = 7482
Step 87: 7482 + 87 = 7569
Step 88: 7569 + 87 = 7656
Step 89: 7656 + 87 = 7743
Step 90: 7743 + 87 = 7830
Step 91: 7830 + 87 = 7917
Step 92: 7917 + 87 = 8004
Step 93: 8004 + 87 = 8091
Step 94: 8091 + 87 = 8178
Step 95: 8178 + 87 = 8265
Step 96: 8265 + 87 = 8352
Step 97: 8352 + 87 = 8439
Step 98: 8439 + 87 = 8526
Step 99: 8526 + 87 = 8613
Step 100: 8613 + 87 = 8700
Step 101: 8700 + 87 = 8787
Step 102: 8787 + 87 = 8874
Step 103: 8874 + 87 = 8961
Step 104: 8961 + 87 = 9048
Step 105: 9048 + 87 = 9135
Step 106: 9135 + 87 = 9222
Step 107: 9222 + 87 = 9309
Step 108: 9309 + 87 = 9396
Step 109: 9396 + 87 = 9483
Step 110: 9483 + 87 = 9570
Step 111: 9570 + 87 = 9657
Step 112: 9657 + 87 = 9744
Step 113: 9744 + 87 = 9831
Step 114: 9831 + 87 = 9918
Step 115: 9918 + 87 = 10005
Step 116: 10005 + 87 = 10092
Step 117: 10092 + 87 = 10179
Step 118: 10179 + 87 = 10266
Step 119: 10266 + 87 = 10353
Step 120: 10353 + 87 = 10440
Step 121: 10440 + 87 = 10527
Step 122: 10527 + 87 = 10614
Step 123: 10614 + 87 = 10701
Step 124: 10701 + 87 = 10788
Step 125: 10788 + 87 = 10875
Step 126: 10875 + 87 = 10962
Step 127: 10962 + 87 = 11049
Step 128: 11049 + 87 = 11136
Step 129: 11136 + 87 = 11223
Step 130: 11223 + 87 = 11310
Step 131: 11310 + 87 = 11397
Step 132: 11397 + 87 = 11484
Step 133: 11484 + 87 = 11571
Step 134: 11571 + 87 = 11658
Step 135: 11658 + 87 = 11745
Step 136: 11745 + 87 = 11832
Step 137: 11832 + 87 = 11919
Step 138: 11919 + 87 = 12006
Step 139: 12006 + 87 = 12093
Step 140: 12093 + 87 = 12180
Step 141: 12180 + 87 = 12267
Step 142: 12267 + 87 = 12354

So, 87*142 = 12354