Let's roll up our sleeves and solve this. We have 42 and we're going to multiply it by 121, essentially adding 42 to itself 121 times.
Step 1: 0 + 42 = 42
Step 2: 42 + 42 = 84
Step 3: 84 + 42 = 126
Step 4: 126 + 42 = 168
Step 5: 168 + 42 = 210
Step 6: 210 + 42 = 252
Step 7: 252 + 42 = 294
Step 8: 294 + 42 = 336
Step 9: 336 + 42 = 378
Step 10: 378 + 42 = 420
Step 11: 420 + 42 = 462
Step 12: 462 + 42 = 504
Step 13: 504 + 42 = 546
Step 14: 546 + 42 = 588
Step 15: 588 + 42 = 630
Step 16: 630 + 42 = 672
Step 17: 672 + 42 = 714
Step 18: 714 + 42 = 756
Step 19: 756 + 42 = 798
Step 20: 798 + 42 = 840
Step 21: 840 + 42 = 882
Step 22: 882 + 42 = 924
Step 23: 924 + 42 = 966
Step 24: 966 + 42 = 1008
Step 25: 1008 + 42 = 1050
Step 26: 1050 + 42 = 1092
Step 27: 1092 + 42 = 1134
Step 28: 1134 + 42 = 1176
Step 29: 1176 + 42 = 1218
Step 30: 1218 + 42 = 1260
Step 31: 1260 + 42 = 1302
Step 32: 1302 + 42 = 1344
Step 33: 1344 + 42 = 1386
Step 34: 1386 + 42 = 1428
Step 35: 1428 + 42 = 1470
Step 36: 1470 + 42 = 1512
Step 37: 1512 + 42 = 1554
Step 38: 1554 + 42 = 1596
Step 39: 1596 + 42 = 1638
Step 40: 1638 + 42 = 1680
Step 41: 1680 + 42 = 1722
Step 42: 1722 + 42 = 1764
Step 43: 1764 + 42 = 1806
Step 44: 1806 + 42 = 1848
Step 45: 1848 + 42 = 1890
Step 46: 1890 + 42 = 1932
Step 47: 1932 + 42 = 1974
Step 48: 1974 + 42 = 2016
Step 49: 2016 + 42 = 2058
Step 50: 2058 + 42 = 2100
Step 51: 2100 + 42 = 2142
Step 52: 2142 + 42 = 2184
Step 53: 2184 + 42 = 2226
Step 54: 2226 + 42 = 2268
Step 55: 2268 + 42 = 2310
Step 56: 2310 + 42 = 2352
Step 57: 2352 + 42 = 2394
Step 58: 2394 + 42 = 2436
Step 59: 2436 + 42 = 2478
Step 60: 2478 + 42 = 2520
Step 61: 2520 + 42 = 2562
Step 62: 2562 + 42 = 2604
Step 63: 2604 + 42 = 2646
Step 64: 2646 + 42 = 2688
Step 65: 2688 + 42 = 2730
Step 66: 2730 + 42 = 2772
Step 67: 2772 + 42 = 2814
Step 68: 2814 + 42 = 2856
Step 69: 2856 + 42 = 2898
Step 70: 2898 + 42 = 2940
Step 71: 2940 + 42 = 2982
Step 72: 2982 + 42 = 3024
Step 73: 3024 + 42 = 3066
Step 74: 3066 + 42 = 3108
Step 75: 3108 + 42 = 3150
Step 76: 3150 + 42 = 3192
Step 77: 3192 + 42 = 3234
Step 78: 3234 + 42 = 3276
Step 79: 3276 + 42 = 3318
Step 80: 3318 + 42 = 3360
Step 81: 3360 + 42 = 3402
Step 82: 3402 + 42 = 3444
Step 83: 3444 + 42 = 3486
Step 84: 3486 + 42 = 3528
Step 85: 3528 + 42 = 3570
Step 86: 3570 + 42 = 3612
Step 87: 3612 + 42 = 3654
Step 88: 3654 + 42 = 3696
Step 89: 3696 + 42 = 3738
Step 90: 3738 + 42 = 3780
Step 91: 3780 + 42 = 3822
Step 92: 3822 + 42 = 3864
Step 93: 3864 + 42 = 3906
Step 94: 3906 + 42 = 3948
Step 95: 3948 + 42 = 3990
Step 96: 3990 + 42 = 4032
Step 97: 4032 + 42 = 4074
Step 98: 4074 + 42 = 4116
Step 99: 4116 + 42 = 4158
Step 100: 4158 + 42 = 4200
Step 101: 4200 + 42 = 4242
Step 102: 4242 + 42 = 4284
Step 103: 4284 + 42 = 4326
Step 104: 4326 + 42 = 4368
Step 105: 4368 + 42 = 4410
Step 106: 4410 + 42 = 4452
Step 107: 4452 + 42 = 4494
Step 108: 4494 + 42 = 4536
Step 109: 4536 + 42 = 4578
Step 110: 4578 + 42 = 4620
Step 111: 4620 + 42 = 4662
Step 112: 4662 + 42 = 4704
Step 113: 4704 + 42 = 4746
Step 114: 4746 + 42 = 4788
Step 115: 4788 + 42 = 4830
Step 116: 4830 + 42 = 4872
Step 117: 4872 + 42 = 4914
Step 118: 4914 + 42 = 4956
Step 119: 4956 + 42 = 4998
Step 120: 4998 + 42 = 5040
Step 121: 5040 + 42 = 5082

So, 42*121 = 5082