Let's roll up our sleeves and solve this. We have 864 and we're going to multiply it by 161, essentially adding 864 to itself 161 times.
Step 1: 0 + 864 = 864
Step 2: 864 + 864 = 1728
Step 3: 1728 + 864 = 2592
Step 4: 2592 + 864 = 3456
Step 5: 3456 + 864 = 4320
Step 6: 4320 + 864 = 5184
Step 7: 5184 + 864 = 6048
Step 8: 6048 + 864 = 6912
Step 9: 6912 + 864 = 7776
Step 10: 7776 + 864 = 8640
Step 11: 8640 + 864 = 9504
Step 12: 9504 + 864 = 10368
Step 13: 10368 + 864 = 11232
Step 14: 11232 + 864 = 12096
Step 15: 12096 + 864 = 12960
Step 16: 12960 + 864 = 13824
Step 17: 13824 + 864 = 14688
Step 18: 14688 + 864 = 15552
Step 19: 15552 + 864 = 16416
Step 20: 16416 + 864 = 17280
Step 21: 17280 + 864 = 18144
Step 22: 18144 + 864 = 19008
Step 23: 19008 + 864 = 19872
Step 24: 19872 + 864 = 20736
Step 25: 20736 + 864 = 21600
Step 26: 21600 + 864 = 22464
Step 27: 22464 + 864 = 23328
Step 28: 23328 + 864 = 24192
Step 29: 24192 + 864 = 25056
Step 30: 25056 + 864 = 25920
Step 31: 25920 + 864 = 26784
Step 32: 26784 + 864 = 27648
Step 33: 27648 + 864 = 28512
Step 34: 28512 + 864 = 29376
Step 35: 29376 + 864 = 30240
Step 36: 30240 + 864 = 31104
Step 37: 31104 + 864 = 31968
Step 38: 31968 + 864 = 32832
Step 39: 32832 + 864 = 33696
Step 40: 33696 + 864 = 34560
Step 41: 34560 + 864 = 35424
Step 42: 35424 + 864 = 36288
Step 43: 36288 + 864 = 37152
Step 44: 37152 + 864 = 38016
Step 45: 38016 + 864 = 38880
Step 46: 38880 + 864 = 39744
Step 47: 39744 + 864 = 40608
Step 48: 40608 + 864 = 41472
Step 49: 41472 + 864 = 42336
Step 50: 42336 + 864 = 43200
Step 51: 43200 + 864 = 44064
Step 52: 44064 + 864 = 44928
Step 53: 44928 + 864 = 45792
Step 54: 45792 + 864 = 46656
Step 55: 46656 + 864 = 47520
Step 56: 47520 + 864 = 48384
Step 57: 48384 + 864 = 49248
Step 58: 49248 + 864 = 50112
Step 59: 50112 + 864 = 50976
Step 60: 50976 + 864 = 51840
Step 61: 51840 + 864 = 52704
Step 62: 52704 + 864 = 53568
Step 63: 53568 + 864 = 54432
Step 64: 54432 + 864 = 55296
Step 65: 55296 + 864 = 56160
Step 66: 56160 + 864 = 57024
Step 67: 57024 + 864 = 57888
Step 68: 57888 + 864 = 58752
Step 69: 58752 + 864 = 59616
Step 70: 59616 + 864 = 60480
Step 71: 60480 + 864 = 61344
Step 72: 61344 + 864 = 62208
Step 73: 62208 + 864 = 63072
Step 74: 63072 + 864 = 63936
Step 75: 63936 + 864 = 64800
Step 76: 64800 + 864 = 65664
Step 77: 65664 + 864 = 66528
Step 78: 66528 + 864 = 67392
Step 79: 67392 + 864 = 68256
Step 80: 68256 + 864 = 69120
Step 81: 69120 + 864 = 69984
Step 82: 69984 + 864 = 70848
Step 83: 70848 + 864 = 71712
Step 84: 71712 + 864 = 72576
Step 85: 72576 + 864 = 73440
Step 86: 73440 + 864 = 74304
Step 87: 74304 + 864 = 75168
Step 88: 75168 + 864 = 76032
Step 89: 76032 + 864 = 76896
Step 90: 76896 + 864 = 77760
Step 91: 77760 + 864 = 78624
Step 92: 78624 + 864 = 79488
Step 93: 79488 + 864 = 80352
Step 94: 80352 + 864 = 81216
Step 95: 81216 + 864 = 82080
Step 96: 82080 + 864 = 82944
Step 97: 82944 + 864 = 83808
Step 98: 83808 + 864 = 84672
Step 99: 84672 + 864 = 85536
Step 100: 85536 + 864 = 86400
Step 101: 86400 + 864 = 87264
Step 102: 87264 + 864 = 88128
Step 103: 88128 + 864 = 88992
Step 104: 88992 + 864 = 89856
Step 105: 89856 + 864 = 90720
Step 106: 90720 + 864 = 91584
Step 107: 91584 + 864 = 92448
Step 108: 92448 + 864 = 93312
Step 109: 93312 + 864 = 94176
Step 110: 94176 + 864 = 95040
Step 111: 95040 + 864 = 95904
Step 112: 95904 + 864 = 96768
Step 113: 96768 + 864 = 97632
Step 114: 97632 + 864 = 98496
Step 115: 98496 + 864 = 99360
Step 116: 99360 + 864 = 100224
Step 117: 100224 + 864 = 101088
Step 118: 101088 + 864 = 101952
Step 119: 101952 + 864 = 102816
Step 120: 102816 + 864 = 103680
Step 121: 103680 + 864 = 104544
Step 122: 104544 + 864 = 105408
Step 123: 105408 + 864 = 106272
Step 124: 106272 + 864 = 107136
Step 125: 107136 + 864 = 108000
Step 126: 108000 + 864 = 108864
Step 127: 108864 + 864 = 109728
Step 128: 109728 + 864 = 110592
Step 129: 110592 + 864 = 111456
Step 130: 111456 + 864 = 112320
Step 131: 112320 + 864 = 113184
Step 132: 113184 + 864 = 114048
Step 133: 114048 + 864 = 114912
Step 134: 114912 + 864 = 115776
Step 135: 115776 + 864 = 116640
Step 136: 116640 + 864 = 117504
Step 137: 117504 + 864 = 118368
Step 138: 118368 + 864 = 119232
Step 139: 119232 + 864 = 120096
Step 140: 120096 + 864 = 120960
Step 141: 120960 + 864 = 121824
Step 142: 121824 + 864 = 122688
Step 143: 122688 + 864 = 123552
Step 144: 123552 + 864 = 124416
Step 145: 124416 + 864 = 125280
Step 146: 125280 + 864 = 126144
Step 147: 126144 + 864 = 127008
Step 148: 127008 + 864 = 127872
Step 149: 127872 + 864 = 128736
Step 150: 128736 + 864 = 129600
Step 151: 129600 + 864 = 130464
Step 152: 130464 + 864 = 131328
Step 153: 131328 + 864 = 132192
Step 154: 132192 + 864 = 133056
Step 155: 133056 + 864 = 133920
Step 156: 133920 + 864 = 134784
Step 157: 134784 + 864 = 135648
Step 158: 135648 + 864 = 136512
Step 159: 136512 + 864 = 137376
Step 160: 137376 + 864 = 138240
Step 161: 138240 + 864 = 139104

So, 864*161 = 139104