Let's roll up our sleeves and solve this. We have 339 and we're going to multiply it by 125, essentially adding 339 to itself 125 times.
Step 1: 0 + 339 = 339
Step 2: 339 + 339 = 678
Step 3: 678 + 339 = 1017
Step 4: 1017 + 339 = 1356
Step 5: 1356 + 339 = 1695
Step 6: 1695 + 339 = 2034
Step 7: 2034 + 339 = 2373
Step 8: 2373 + 339 = 2712
Step 9: 2712 + 339 = 3051
Step 10: 3051 + 339 = 3390
Step 11: 3390 + 339 = 3729
Step 12: 3729 + 339 = 4068
Step 13: 4068 + 339 = 4407
Step 14: 4407 + 339 = 4746
Step 15: 4746 + 339 = 5085
Step 16: 5085 + 339 = 5424
Step 17: 5424 + 339 = 5763
Step 18: 5763 + 339 = 6102
Step 19: 6102 + 339 = 6441
Step 20: 6441 + 339 = 6780
Step 21: 6780 + 339 = 7119
Step 22: 7119 + 339 = 7458
Step 23: 7458 + 339 = 7797
Step 24: 7797 + 339 = 8136
Step 25: 8136 + 339 = 8475
Step 26: 8475 + 339 = 8814
Step 27: 8814 + 339 = 9153
Step 28: 9153 + 339 = 9492
Step 29: 9492 + 339 = 9831
Step 30: 9831 + 339 = 10170
Step 31: 10170 + 339 = 10509
Step 32: 10509 + 339 = 10848
Step 33: 10848 + 339 = 11187
Step 34: 11187 + 339 = 11526
Step 35: 11526 + 339 = 11865
Step 36: 11865 + 339 = 12204
Step 37: 12204 + 339 = 12543
Step 38: 12543 + 339 = 12882
Step 39: 12882 + 339 = 13221
Step 40: 13221 + 339 = 13560
Step 41: 13560 + 339 = 13899
Step 42: 13899 + 339 = 14238
Step 43: 14238 + 339 = 14577
Step 44: 14577 + 339 = 14916
Step 45: 14916 + 339 = 15255
Step 46: 15255 + 339 = 15594
Step 47: 15594 + 339 = 15933
Step 48: 15933 + 339 = 16272
Step 49: 16272 + 339 = 16611
Step 50: 16611 + 339 = 16950
Step 51: 16950 + 339 = 17289
Step 52: 17289 + 339 = 17628
Step 53: 17628 + 339 = 17967
Step 54: 17967 + 339 = 18306
Step 55: 18306 + 339 = 18645
Step 56: 18645 + 339 = 18984
Step 57: 18984 + 339 = 19323
Step 58: 19323 + 339 = 19662
Step 59: 19662 + 339 = 20001
Step 60: 20001 + 339 = 20340
Step 61: 20340 + 339 = 20679
Step 62: 20679 + 339 = 21018
Step 63: 21018 + 339 = 21357
Step 64: 21357 + 339 = 21696
Step 65: 21696 + 339 = 22035
Step 66: 22035 + 339 = 22374
Step 67: 22374 + 339 = 22713
Step 68: 22713 + 339 = 23052
Step 69: 23052 + 339 = 23391
Step 70: 23391 + 339 = 23730
Step 71: 23730 + 339 = 24069
Step 72: 24069 + 339 = 24408
Step 73: 24408 + 339 = 24747
Step 74: 24747 + 339 = 25086
Step 75: 25086 + 339 = 25425
Step 76: 25425 + 339 = 25764
Step 77: 25764 + 339 = 26103
Step 78: 26103 + 339 = 26442
Step 79: 26442 + 339 = 26781
Step 80: 26781 + 339 = 27120
Step 81: 27120 + 339 = 27459
Step 82: 27459 + 339 = 27798
Step 83: 27798 + 339 = 28137
Step 84: 28137 + 339 = 28476
Step 85: 28476 + 339 = 28815
Step 86: 28815 + 339 = 29154
Step 87: 29154 + 339 = 29493
Step 88: 29493 + 339 = 29832
Step 89: 29832 + 339 = 30171
Step 90: 30171 + 339 = 30510
Step 91: 30510 + 339 = 30849
Step 92: 30849 + 339 = 31188
Step 93: 31188 + 339 = 31527
Step 94: 31527 + 339 = 31866
Step 95: 31866 + 339 = 32205
Step 96: 32205 + 339 = 32544
Step 97: 32544 + 339 = 32883
Step 98: 32883 + 339 = 33222
Step 99: 33222 + 339 = 33561
Step 100: 33561 + 339 = 33900
Step 101: 33900 + 339 = 34239
Step 102: 34239 + 339 = 34578
Step 103: 34578 + 339 = 34917
Step 104: 34917 + 339 = 35256
Step 105: 35256 + 339 = 35595
Step 106: 35595 + 339 = 35934
Step 107: 35934 + 339 = 36273
Step 108: 36273 + 339 = 36612
Step 109: 36612 + 339 = 36951
Step 110: 36951 + 339 = 37290
Step 111: 37290 + 339 = 37629
Step 112: 37629 + 339 = 37968
Step 113: 37968 + 339 = 38307
Step 114: 38307 + 339 = 38646
Step 115: 38646 + 339 = 38985
Step 116: 38985 + 339 = 39324
Step 117: 39324 + 339 = 39663
Step 118: 39663 + 339 = 40002
Step 119: 40002 + 339 = 40341
Step 120: 40341 + 339 = 40680
Step 121: 40680 + 339 = 41019
Step 122: 41019 + 339 = 41358
Step 123: 41358 + 339 = 41697
Step 124: 41697 + 339 = 42036
Step 125: 42036 + 339 = 42375

So, 339*125 = 42375