OK, let's work through this together. We're starting with 684 and we're going to multiply it by 64, which means we add 684 to itself 64 times.
Step 1: 0 + 684 = 684
Step 2: 684 + 684 = 1368
Step 3: 1368 + 684 = 2052
Step 4: 2052 + 684 = 2736
Step 5: 2736 + 684 = 3420
Step 6: 3420 + 684 = 4104
Step 7: 4104 + 684 = 4788
Step 8: 4788 + 684 = 5472
Step 9: 5472 + 684 = 6156
Step 10: 6156 + 684 = 6840
Step 11: 6840 + 684 = 7524
Step 12: 7524 + 684 = 8208
Step 13: 8208 + 684 = 8892
Step 14: 8892 + 684 = 9576
Step 15: 9576 + 684 = 10260
Step 16: 10260 + 684 = 10944
Step 17: 10944 + 684 = 11628
Step 18: 11628 + 684 = 12312
Step 19: 12312 + 684 = 12996
Step 20: 12996 + 684 = 13680
Step 21: 13680 + 684 = 14364
Step 22: 14364 + 684 = 15048
Step 23: 15048 + 684 = 15732
Step 24: 15732 + 684 = 16416
Step 25: 16416 + 684 = 17100
Step 26: 17100 + 684 = 17784
Step 27: 17784 + 684 = 18468
Step 28: 18468 + 684 = 19152
Step 29: 19152 + 684 = 19836
Step 30: 19836 + 684 = 20520
Step 31: 20520 + 684 = 21204
Step 32: 21204 + 684 = 21888
Step 33: 21888 + 684 = 22572
Step 34: 22572 + 684 = 23256
Step 35: 23256 + 684 = 23940
Step 36: 23940 + 684 = 24624
Step 37: 24624 + 684 = 25308
Step 38: 25308 + 684 = 25992
Step 39: 25992 + 684 = 26676
Step 40: 26676 + 684 = 27360
Step 41: 27360 + 684 = 28044
Step 42: 28044 + 684 = 28728
Step 43: 28728 + 684 = 29412
Step 44: 29412 + 684 = 30096
Step 45: 30096 + 684 = 30780
Step 46: 30780 + 684 = 31464
Step 47: 31464 + 684 = 32148
Step 48: 32148 + 684 = 32832
Step 49: 32832 + 684 = 33516
Step 50: 33516 + 684 = 34200
Step 51: 34200 + 684 = 34884
Step 52: 34884 + 684 = 35568
Step 53: 35568 + 684 = 36252
Step 54: 36252 + 684 = 36936
Step 55: 36936 + 684 = 37620
Step 56: 37620 + 684 = 38304
Step 57: 38304 + 684 = 38988
Step 58: 38988 + 684 = 39672
Step 59: 39672 + 684 = 40356
Step 60: 40356 + 684 = 41040
Step 61: 41040 + 684 = 41724
Step 62: 41724 + 684 = 42408
Step 63: 42408 + 684 = 43092
Step 64: 43092 + 684 = 43776

So, 684*64 = 43776