OK, let's work through this together. We're starting with 678 and we're going to multiply it by 243, which means we add 678 to itself 243 times.
Step 1: 0 + 678 = 678
Step 2: 678 + 678 = 1356
Step 3: 1356 + 678 = 2034
Step 4: 2034 + 678 = 2712
Step 5: 2712 + 678 = 3390
Step 6: 3390 + 678 = 4068
Step 7: 4068 + 678 = 4746
Step 8: 4746 + 678 = 5424
Step 9: 5424 + 678 = 6102
Step 10: 6102 + 678 = 6780
Step 11: 6780 + 678 = 7458
Step 12: 7458 + 678 = 8136
Step 13: 8136 + 678 = 8814
Step 14: 8814 + 678 = 9492
Step 15: 9492 + 678 = 10170
Step 16: 10170 + 678 = 10848
Step 17: 10848 + 678 = 11526
Step 18: 11526 + 678 = 12204
Step 19: 12204 + 678 = 12882
Step 20: 12882 + 678 = 13560
Step 21: 13560 + 678 = 14238
Step 22: 14238 + 678 = 14916
Step 23: 14916 + 678 = 15594
Step 24: 15594 + 678 = 16272
Step 25: 16272 + 678 = 16950
Step 26: 16950 + 678 = 17628
Step 27: 17628 + 678 = 18306
Step 28: 18306 + 678 = 18984
Step 29: 18984 + 678 = 19662
Step 30: 19662 + 678 = 20340
Step 31: 20340 + 678 = 21018
Step 32: 21018 + 678 = 21696
Step 33: 21696 + 678 = 22374
Step 34: 22374 + 678 = 23052
Step 35: 23052 + 678 = 23730
Step 36: 23730 + 678 = 24408
Step 37: 24408 + 678 = 25086
Step 38: 25086 + 678 = 25764
Step 39: 25764 + 678 = 26442
Step 40: 26442 + 678 = 27120
Step 41: 27120 + 678 = 27798
Step 42: 27798 + 678 = 28476
Step 43: 28476 + 678 = 29154
Step 44: 29154 + 678 = 29832
Step 45: 29832 + 678 = 30510
Step 46: 30510 + 678 = 31188
Step 47: 31188 + 678 = 31866
Step 48: 31866 + 678 = 32544
Step 49: 32544 + 678 = 33222
Step 50: 33222 + 678 = 33900
Step 51: 33900 + 678 = 34578
Step 52: 34578 + 678 = 35256
Step 53: 35256 + 678 = 35934
Step 54: 35934 + 678 = 36612
Step 55: 36612 + 678 = 37290
Step 56: 37290 + 678 = 37968
Step 57: 37968 + 678 = 38646
Step 58: 38646 + 678 = 39324
Step 59: 39324 + 678 = 40002
Step 60: 40002 + 678 = 40680
Step 61: 40680 + 678 = 41358
Step 62: 41358 + 678 = 42036
Step 63: 42036 + 678 = 42714
Step 64: 42714 + 678 = 43392
Step 65: 43392 + 678 = 44070
Step 66: 44070 + 678 = 44748
Step 67: 44748 + 678 = 45426
Step 68: 45426 + 678 = 46104
Step 69: 46104 + 678 = 46782
Step 70: 46782 + 678 = 47460
Step 71: 47460 + 678 = 48138
Step 72: 48138 + 678 = 48816
Step 73: 48816 + 678 = 49494
Step 74: 49494 + 678 = 50172
Step 75: 50172 + 678 = 50850
Step 76: 50850 + 678 = 51528
Step 77: 51528 + 678 = 52206
Step 78: 52206 + 678 = 52884
Step 79: 52884 + 678 = 53562
Step 80: 53562 + 678 = 54240
Step 81: 54240 + 678 = 54918
Step 82: 54918 + 678 = 55596
Step 83: 55596 + 678 = 56274
Step 84: 56274 + 678 = 56952
Step 85: 56952 + 678 = 57630
Step 86: 57630 + 678 = 58308
Step 87: 58308 + 678 = 58986
Step 88: 58986 + 678 = 59664
Step 89: 59664 + 678 = 60342
Step 90: 60342 + 678 = 61020
Step 91: 61020 + 678 = 61698
Step 92: 61698 + 678 = 62376
Step 93: 62376 + 678 = 63054
Step 94: 63054 + 678 = 63732
Step 95: 63732 + 678 = 64410
Step 96: 64410 + 678 = 65088
Step 97: 65088 + 678 = 65766
Step 98: 65766 + 678 = 66444
Step 99: 66444 + 678 = 67122
Step 100: 67122 + 678 = 67800
Step 101: 67800 + 678 = 68478
Step 102: 68478 + 678 = 69156
Step 103: 69156 + 678 = 69834
Step 104: 69834 + 678 = 70512
Step 105: 70512 + 678 = 71190
Step 106: 71190 + 678 = 71868
Step 107: 71868 + 678 = 72546
Step 108: 72546 + 678 = 73224
Step 109: 73224 + 678 = 73902
Step 110: 73902 + 678 = 74580
Step 111: 74580 + 678 = 75258
Step 112: 75258 + 678 = 75936
Step 113: 75936 + 678 = 76614
Step 114: 76614 + 678 = 77292
Step 115: 77292 + 678 = 77970
Step 116: 77970 + 678 = 78648
Step 117: 78648 + 678 = 79326
Step 118: 79326 + 678 = 80004
Step 119: 80004 + 678 = 80682
Step 120: 80682 + 678 = 81360
Step 121: 81360 + 678 = 82038
Step 122: 82038 + 678 = 82716
Step 123: 82716 + 678 = 83394
Step 124: 83394 + 678 = 84072
Step 125: 84072 + 678 = 84750
Step 126: 84750 + 678 = 85428
Step 127: 85428 + 678 = 86106
Step 128: 86106 + 678 = 86784
Step 129: 86784 + 678 = 87462
Step 130: 87462 + 678 = 88140
Step 131: 88140 + 678 = 88818
Step 132: 88818 + 678 = 89496
Step 133: 89496 + 678 = 90174
Step 134: 90174 + 678 = 90852
Step 135: 90852 + 678 = 91530
Step 136: 91530 + 678 = 92208
Step 137: 92208 + 678 = 92886
Step 138: 92886 + 678 = 93564
Step 139: 93564 + 678 = 94242
Step 140: 94242 + 678 = 94920
Step 141: 94920 + 678 = 95598
Step 142: 95598 + 678 = 96276
Step 143: 96276 + 678 = 96954
Step 144: 96954 + 678 = 97632
Step 145: 97632 + 678 = 98310
Step 146: 98310 + 678 = 98988
Step 147: 98988 + 678 = 99666
Step 148: 99666 + 678 = 100344
Step 149: 100344 + 678 = 101022
Step 150: 101022 + 678 = 101700
Step 151: 101700 + 678 = 102378
Step 152: 102378 + 678 = 103056
Step 153: 103056 + 678 = 103734
Step 154: 103734 + 678 = 104412
Step 155: 104412 + 678 = 105090
Step 156: 105090 + 678 = 105768
Step 157: 105768 + 678 = 106446
Step 158: 106446 + 678 = 107124
Step 159: 107124 + 678 = 107802
Step 160: 107802 + 678 = 108480
Step 161: 108480 + 678 = 109158
Step 162: 109158 + 678 = 109836
Step 163: 109836 + 678 = 110514
Step 164: 110514 + 678 = 111192
Step 165: 111192 + 678 = 111870
Step 166: 111870 + 678 = 112548
Step 167: 112548 + 678 = 113226
Step 168: 113226 + 678 = 113904
Step 169: 113904 + 678 = 114582
Step 170: 114582 + 678 = 115260
Step 171: 115260 + 678 = 115938
Step 172: 115938 + 678 = 116616
Step 173: 116616 + 678 = 117294
Step 174: 117294 + 678 = 117972
Step 175: 117972 + 678 = 118650
Step 176: 118650 + 678 = 119328
Step 177: 119328 + 678 = 120006
Step 178: 120006 + 678 = 120684
Step 179: 120684 + 678 = 121362
Step 180: 121362 + 678 = 122040
Step 181: 122040 + 678 = 122718
Step 182: 122718 + 678 = 123396
Step 183: 123396 + 678 = 124074
Step 184: 124074 + 678 = 124752
Step 185: 124752 + 678 = 125430
Step 186: 125430 + 678 = 126108
Step 187: 126108 + 678 = 126786
Step 188: 126786 + 678 = 127464
Step 189: 127464 + 678 = 128142
Step 190: 128142 + 678 = 128820
Step 191: 128820 + 678 = 129498
Step 192: 129498 + 678 = 130176
Step 193: 130176 + 678 = 130854
Step 194: 130854 + 678 = 131532
Step 195: 131532 + 678 = 132210
Step 196: 132210 + 678 = 132888
Step 197: 132888 + 678 = 133566
Step 198: 133566 + 678 = 134244
Step 199: 134244 + 678 = 134922
Step 200: 134922 + 678 = 135600
Step 201: 135600 + 678 = 136278
Step 202: 136278 + 678 = 136956
Step 203: 136956 + 678 = 137634
Step 204: 137634 + 678 = 138312
Step 205: 138312 + 678 = 138990
Step 206: 138990 + 678 = 139668
Step 207: 139668 + 678 = 140346
Step 208: 140346 + 678 = 141024
Step 209: 141024 + 678 = 141702
Step 210: 141702 + 678 = 142380
Step 211: 142380 + 678 = 143058
Step 212: 143058 + 678 = 143736
Step 213: 143736 + 678 = 144414
Step 214: 144414 + 678 = 145092
Step 215: 145092 + 678 = 145770
Step 216: 145770 + 678 = 146448
Step 217: 146448 + 678 = 147126
Step 218: 147126 + 678 = 147804
Step 219: 147804 + 678 = 148482
Step 220: 148482 + 678 = 149160
Step 221: 149160 + 678 = 149838
Step 222: 149838 + 678 = 150516
Step 223: 150516 + 678 = 151194
Step 224: 151194 + 678 = 151872
Step 225: 151872 + 678 = 152550
Step 226: 152550 + 678 = 153228
Step 227: 153228 + 678 = 153906
Step 228: 153906 + 678 = 154584
Step 229: 154584 + 678 = 155262
Step 230: 155262 + 678 = 155940
Step 231: 155940 + 678 = 156618
Step 232: 156618 + 678 = 157296
Step 233: 157296 + 678 = 157974
Step 234: 157974 + 678 = 158652
Step 235: 158652 + 678 = 159330
Step 236: 159330 + 678 = 160008
Step 237: 160008 + 678 = 160686
Step 238: 160686 + 678 = 161364
Step 239: 161364 + 678 = 162042
Step 240: 162042 + 678 = 162720
Step 241: 162720 + 678 = 163398
Step 242: 163398 + 678 = 164076
Step 243: 164076 + 678 = 164754

So, 678*243 = 164754