OK, let's work through this together. We're starting with 851 and we're going to multiply it by 158, which means we add 851 to itself 158 times.
Step 1: 0 + 851 = 851
Step 2: 851 + 851 = 1702
Step 3: 1702 + 851 = 2553
Step 4: 2553 + 851 = 3404
Step 5: 3404 + 851 = 4255
Step 6: 4255 + 851 = 5106
Step 7: 5106 + 851 = 5957
Step 8: 5957 + 851 = 6808
Step 9: 6808 + 851 = 7659
Step 10: 7659 + 851 = 8510
Step 11: 8510 + 851 = 9361
Step 12: 9361 + 851 = 10212
Step 13: 10212 + 851 = 11063
Step 14: 11063 + 851 = 11914
Step 15: 11914 + 851 = 12765
Step 16: 12765 + 851 = 13616
Step 17: 13616 + 851 = 14467
Step 18: 14467 + 851 = 15318
Step 19: 15318 + 851 = 16169
Step 20: 16169 + 851 = 17020
Step 21: 17020 + 851 = 17871
Step 22: 17871 + 851 = 18722
Step 23: 18722 + 851 = 19573
Step 24: 19573 + 851 = 20424
Step 25: 20424 + 851 = 21275
Step 26: 21275 + 851 = 22126
Step 27: 22126 + 851 = 22977
Step 28: 22977 + 851 = 23828
Step 29: 23828 + 851 = 24679
Step 30: 24679 + 851 = 25530
Step 31: 25530 + 851 = 26381
Step 32: 26381 + 851 = 27232
Step 33: 27232 + 851 = 28083
Step 34: 28083 + 851 = 28934
Step 35: 28934 + 851 = 29785
Step 36: 29785 + 851 = 30636
Step 37: 30636 + 851 = 31487
Step 38: 31487 + 851 = 32338
Step 39: 32338 + 851 = 33189
Step 40: 33189 + 851 = 34040
Step 41: 34040 + 851 = 34891
Step 42: 34891 + 851 = 35742
Step 43: 35742 + 851 = 36593
Step 44: 36593 + 851 = 37444
Step 45: 37444 + 851 = 38295
Step 46: 38295 + 851 = 39146
Step 47: 39146 + 851 = 39997
Step 48: 39997 + 851 = 40848
Step 49: 40848 + 851 = 41699
Step 50: 41699 + 851 = 42550
Step 51: 42550 + 851 = 43401
Step 52: 43401 + 851 = 44252
Step 53: 44252 + 851 = 45103
Step 54: 45103 + 851 = 45954
Step 55: 45954 + 851 = 46805
Step 56: 46805 + 851 = 47656
Step 57: 47656 + 851 = 48507
Step 58: 48507 + 851 = 49358
Step 59: 49358 + 851 = 50209
Step 60: 50209 + 851 = 51060
Step 61: 51060 + 851 = 51911
Step 62: 51911 + 851 = 52762
Step 63: 52762 + 851 = 53613
Step 64: 53613 + 851 = 54464
Step 65: 54464 + 851 = 55315
Step 66: 55315 + 851 = 56166
Step 67: 56166 + 851 = 57017
Step 68: 57017 + 851 = 57868
Step 69: 57868 + 851 = 58719
Step 70: 58719 + 851 = 59570
Step 71: 59570 + 851 = 60421
Step 72: 60421 + 851 = 61272
Step 73: 61272 + 851 = 62123
Step 74: 62123 + 851 = 62974
Step 75: 62974 + 851 = 63825
Step 76: 63825 + 851 = 64676
Step 77: 64676 + 851 = 65527
Step 78: 65527 + 851 = 66378
Step 79: 66378 + 851 = 67229
Step 80: 67229 + 851 = 68080
Step 81: 68080 + 851 = 68931
Step 82: 68931 + 851 = 69782
Step 83: 69782 + 851 = 70633
Step 84: 70633 + 851 = 71484
Step 85: 71484 + 851 = 72335
Step 86: 72335 + 851 = 73186
Step 87: 73186 + 851 = 74037
Step 88: 74037 + 851 = 74888
Step 89: 74888 + 851 = 75739
Step 90: 75739 + 851 = 76590
Step 91: 76590 + 851 = 77441
Step 92: 77441 + 851 = 78292
Step 93: 78292 + 851 = 79143
Step 94: 79143 + 851 = 79994
Step 95: 79994 + 851 = 80845
Step 96: 80845 + 851 = 81696
Step 97: 81696 + 851 = 82547
Step 98: 82547 + 851 = 83398
Step 99: 83398 + 851 = 84249
Step 100: 84249 + 851 = 85100
Step 101: 85100 + 851 = 85951
Step 102: 85951 + 851 = 86802
Step 103: 86802 + 851 = 87653
Step 104: 87653 + 851 = 88504
Step 105: 88504 + 851 = 89355
Step 106: 89355 + 851 = 90206
Step 107: 90206 + 851 = 91057
Step 108: 91057 + 851 = 91908
Step 109: 91908 + 851 = 92759
Step 110: 92759 + 851 = 93610
Step 111: 93610 + 851 = 94461
Step 112: 94461 + 851 = 95312
Step 113: 95312 + 851 = 96163
Step 114: 96163 + 851 = 97014
Step 115: 97014 + 851 = 97865
Step 116: 97865 + 851 = 98716
Step 117: 98716 + 851 = 99567
Step 118: 99567 + 851 = 100418
Step 119: 100418 + 851 = 101269
Step 120: 101269 + 851 = 102120
Step 121: 102120 + 851 = 102971
Step 122: 102971 + 851 = 103822
Step 123: 103822 + 851 = 104673
Step 124: 104673 + 851 = 105524
Step 125: 105524 + 851 = 106375
Step 126: 106375 + 851 = 107226
Step 127: 107226 + 851 = 108077
Step 128: 108077 + 851 = 108928
Step 129: 108928 + 851 = 109779
Step 130: 109779 + 851 = 110630
Step 131: 110630 + 851 = 111481
Step 132: 111481 + 851 = 112332
Step 133: 112332 + 851 = 113183
Step 134: 113183 + 851 = 114034
Step 135: 114034 + 851 = 114885
Step 136: 114885 + 851 = 115736
Step 137: 115736 + 851 = 116587
Step 138: 116587 + 851 = 117438
Step 139: 117438 + 851 = 118289
Step 140: 118289 + 851 = 119140
Step 141: 119140 + 851 = 119991
Step 142: 119991 + 851 = 120842
Step 143: 120842 + 851 = 121693
Step 144: 121693 + 851 = 122544
Step 145: 122544 + 851 = 123395
Step 146: 123395 + 851 = 124246
Step 147: 124246 + 851 = 125097
Step 148: 125097 + 851 = 125948
Step 149: 125948 + 851 = 126799
Step 150: 126799 + 851 = 127650
Step 151: 127650 + 851 = 128501
Step 152: 128501 + 851 = 129352
Step 153: 129352 + 851 = 130203
Step 154: 130203 + 851 = 131054
Step 155: 131054 + 851 = 131905
Step 156: 131905 + 851 = 132756
Step 157: 132756 + 851 = 133607
Step 158: 133607 + 851 = 134458

So, 851*158 = 134458