OK, let's work through this together. We're starting with 624 and we're going to multiply it by 84, which means we add 624 to itself 84 times.
Step 1: 0 + 624 = 624
Step 2: 624 + 624 = 1248
Step 3: 1248 + 624 = 1872
Step 4: 1872 + 624 = 2496
Step 5: 2496 + 624 = 3120
Step 6: 3120 + 624 = 3744
Step 7: 3744 + 624 = 4368
Step 8: 4368 + 624 = 4992
Step 9: 4992 + 624 = 5616
Step 10: 5616 + 624 = 6240
Step 11: 6240 + 624 = 6864
Step 12: 6864 + 624 = 7488
Step 13: 7488 + 624 = 8112
Step 14: 8112 + 624 = 8736
Step 15: 8736 + 624 = 9360
Step 16: 9360 + 624 = 9984
Step 17: 9984 + 624 = 10608
Step 18: 10608 + 624 = 11232
Step 19: 11232 + 624 = 11856
Step 20: 11856 + 624 = 12480
Step 21: 12480 + 624 = 13104
Step 22: 13104 + 624 = 13728
Step 23: 13728 + 624 = 14352
Step 24: 14352 + 624 = 14976
Step 25: 14976 + 624 = 15600
Step 26: 15600 + 624 = 16224
Step 27: 16224 + 624 = 16848
Step 28: 16848 + 624 = 17472
Step 29: 17472 + 624 = 18096
Step 30: 18096 + 624 = 18720
Step 31: 18720 + 624 = 19344
Step 32: 19344 + 624 = 19968
Step 33: 19968 + 624 = 20592
Step 34: 20592 + 624 = 21216
Step 35: 21216 + 624 = 21840
Step 36: 21840 + 624 = 22464
Step 37: 22464 + 624 = 23088
Step 38: 23088 + 624 = 23712
Step 39: 23712 + 624 = 24336
Step 40: 24336 + 624 = 24960
Step 41: 24960 + 624 = 25584
Step 42: 25584 + 624 = 26208
Step 43: 26208 + 624 = 26832
Step 44: 26832 + 624 = 27456
Step 45: 27456 + 624 = 28080
Step 46: 28080 + 624 = 28704
Step 47: 28704 + 624 = 29328
Step 48: 29328 + 624 = 29952
Step 49: 29952 + 624 = 30576
Step 50: 30576 + 624 = 31200
Step 51: 31200 + 624 = 31824
Step 52: 31824 + 624 = 32448
Step 53: 32448 + 624 = 33072
Step 54: 33072 + 624 = 33696
Step 55: 33696 + 624 = 34320
Step 56: 34320 + 624 = 34944
Step 57: 34944 + 624 = 35568
Step 58: 35568 + 624 = 36192
Step 59: 36192 + 624 = 36816
Step 60: 36816 + 624 = 37440
Step 61: 37440 + 624 = 38064
Step 62: 38064 + 624 = 38688
Step 63: 38688 + 624 = 39312
Step 64: 39312 + 624 = 39936
Step 65: 39936 + 624 = 40560
Step 66: 40560 + 624 = 41184
Step 67: 41184 + 624 = 41808
Step 68: 41808 + 624 = 42432
Step 69: 42432 + 624 = 43056
Step 70: 43056 + 624 = 43680
Step 71: 43680 + 624 = 44304
Step 72: 44304 + 624 = 44928
Step 73: 44928 + 624 = 45552
Step 74: 45552 + 624 = 46176
Step 75: 46176 + 624 = 46800
Step 76: 46800 + 624 = 47424
Step 77: 47424 + 624 = 48048
Step 78: 48048 + 624 = 48672
Step 79: 48672 + 624 = 49296
Step 80: 49296 + 624 = 49920
Step 81: 49920 + 624 = 50544
Step 82: 50544 + 624 = 51168
Step 83: 51168 + 624 = 51792
Step 84: 51792 + 624 = 52416

So, 624*84 = 52416