Alright, let's solve this math problem step by step. First, we have the number 642. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 78. So, we're going to take the number 642 and add it to itself 78 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

So, 642*78 = 50076