OK, let's work through this together. We're starting with 688 and we're going to multiply it by 72, which means we add 688 to itself 72 times.
Step 1: 0 + 688 = 688
Step 2: 688 + 688 = 1376
Step 3: 1376 + 688 = 2064
Step 4: 2064 + 688 = 2752
Step 5: 2752 + 688 = 3440
Step 6: 3440 + 688 = 4128
Step 7: 4128 + 688 = 4816
Step 8: 4816 + 688 = 5504
Step 9: 5504 + 688 = 6192
Step 10: 6192 + 688 = 6880
Step 11: 6880 + 688 = 7568
Step 12: 7568 + 688 = 8256
Step 13: 8256 + 688 = 8944
Step 14: 8944 + 688 = 9632
Step 15: 9632 + 688 = 10320
Step 16: 10320 + 688 = 11008
Step 17: 11008 + 688 = 11696
Step 18: 11696 + 688 = 12384
Step 19: 12384 + 688 = 13072
Step 20: 13072 + 688 = 13760
Step 21: 13760 + 688 = 14448
Step 22: 14448 + 688 = 15136
Step 23: 15136 + 688 = 15824
Step 24: 15824 + 688 = 16512
Step 25: 16512 + 688 = 17200
Step 26: 17200 + 688 = 17888
Step 27: 17888 + 688 = 18576
Step 28: 18576 + 688 = 19264
Step 29: 19264 + 688 = 19952
Step 30: 19952 + 688 = 20640
Step 31: 20640 + 688 = 21328
Step 32: 21328 + 688 = 22016
Step 33: 22016 + 688 = 22704
Step 34: 22704 + 688 = 23392
Step 35: 23392 + 688 = 24080
Step 36: 24080 + 688 = 24768
Step 37: 24768 + 688 = 25456
Step 38: 25456 + 688 = 26144
Step 39: 26144 + 688 = 26832
Step 40: 26832 + 688 = 27520
Step 41: 27520 + 688 = 28208
Step 42: 28208 + 688 = 28896
Step 43: 28896 + 688 = 29584
Step 44: 29584 + 688 = 30272
Step 45: 30272 + 688 = 30960
Step 46: 30960 + 688 = 31648
Step 47: 31648 + 688 = 32336
Step 48: 32336 + 688 = 33024
Step 49: 33024 + 688 = 33712
Step 50: 33712 + 688 = 34400
Step 51: 34400 + 688 = 35088
Step 52: 35088 + 688 = 35776
Step 53: 35776 + 688 = 36464
Step 54: 36464 + 688 = 37152
Step 55: 37152 + 688 = 37840
Step 56: 37840 + 688 = 38528
Step 57: 38528 + 688 = 39216
Step 58: 39216 + 688 = 39904
Step 59: 39904 + 688 = 40592
Step 60: 40592 + 688 = 41280
Step 61: 41280 + 688 = 41968
Step 62: 41968 + 688 = 42656
Step 63: 42656 + 688 = 43344
Step 64: 43344 + 688 = 44032
Step 65: 44032 + 688 = 44720
Step 66: 44720 + 688 = 45408
Step 67: 45408 + 688 = 46096
Step 68: 46096 + 688 = 46784
Step 69: 46784 + 688 = 47472
Step 70: 47472 + 688 = 48160
Step 71: 48160 + 688 = 48848
Step 72: 48848 + 688 = 49536

So, 688*72 = 49536