Sure thing, let's get straight to it. We start with 642 and we're going to multiply it by 87, which means adding 642 to itself 87 times.
Step 1: 0 + 642 = 642
Step 2: 642 + 642 = 1284
Step 3: 1284 + 642 = 1926
Step 4: 1926 + 642 = 2568
Step 5: 2568 + 642 = 3210
Step 6: 3210 + 642 = 3852
Step 7: 3852 + 642 = 4494
Step 8: 4494 + 642 = 5136
Step 9: 5136 + 642 = 5778
Step 10: 5778 + 642 = 6420
Step 11: 6420 + 642 = 7062
Step 12: 7062 + 642 = 7704
Step 13: 7704 + 642 = 8346
Step 14: 8346 + 642 = 8988
Step 15: 8988 + 642 = 9630
Step 16: 9630 + 642 = 10272
Step 17: 10272 + 642 = 10914
Step 18: 10914 + 642 = 11556
Step 19: 11556 + 642 = 12198
Step 20: 12198 + 642 = 12840
Step 21: 12840 + 642 = 13482
Step 22: 13482 + 642 = 14124
Step 23: 14124 + 642 = 14766
Step 24: 14766 + 642 = 15408
Step 25: 15408 + 642 = 16050
Step 26: 16050 + 642 = 16692
Step 27: 16692 + 642 = 17334
Step 28: 17334 + 642 = 17976
Step 29: 17976 + 642 = 18618
Step 30: 18618 + 642 = 19260
Step 31: 19260 + 642 = 19902
Step 32: 19902 + 642 = 20544
Step 33: 20544 + 642 = 21186
Step 34: 21186 + 642 = 21828
Step 35: 21828 + 642 = 22470
Step 36: 22470 + 642 = 23112
Step 37: 23112 + 642 = 23754
Step 38: 23754 + 642 = 24396
Step 39: 24396 + 642 = 25038
Step 40: 25038 + 642 = 25680
Step 41: 25680 + 642 = 26322
Step 42: 26322 + 642 = 26964
Step 43: 26964 + 642 = 27606
Step 44: 27606 + 642 = 28248
Step 45: 28248 + 642 = 28890
Step 46: 28890 + 642 = 29532
Step 47: 29532 + 642 = 30174
Step 48: 30174 + 642 = 30816
Step 49: 30816 + 642 = 31458
Step 50: 31458 + 642 = 32100
Step 51: 32100 + 642 = 32742
Step 52: 32742 + 642 = 33384
Step 53: 33384 + 642 = 34026
Step 54: 34026 + 642 = 34668
Step 55: 34668 + 642 = 35310
Step 56: 35310 + 642 = 35952
Step 57: 35952 + 642 = 36594
Step 58: 36594 + 642 = 37236
Step 59: 37236 + 642 = 37878
Step 60: 37878 + 642 = 38520
Step 61: 38520 + 642 = 39162
Step 62: 39162 + 642 = 39804
Step 63: 39804 + 642 = 40446
Step 64: 40446 + 642 = 41088
Step 65: 41088 + 642 = 41730
Step 66: 41730 + 642 = 42372
Step 67: 42372 + 642 = 43014
Step 68: 43014 + 642 = 43656
Step 69: 43656 + 642 = 44298
Step 70: 44298 + 642 = 44940
Step 71: 44940 + 642 = 45582
Step 72: 45582 + 642 = 46224
Step 73: 46224 + 642 = 46866
Step 74: 46866 + 642 = 47508
Step 75: 47508 + 642 = 48150
Step 76: 48150 + 642 = 48792
Step 77: 48792 + 642 = 49434
Step 78: 49434 + 642 = 50076
Step 79: 50076 + 642 = 50718
Step 80: 50718 + 642 = 51360
Step 81: 51360 + 642 = 52002
Step 82: 52002 + 642 = 52644
Step 83: 52644 + 642 = 53286
Step 84: 53286 + 642 = 53928
Step 85: 53928 + 642 = 54570
Step 86: 54570 + 642 = 55212
Step 87: 55212 + 642 = 55854

So, 642*87 = 55854