Alright, let's solve this math problem step by step. First, we have the number 639. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 136. So, we're going to take the number 639 and add it to itself 136 times.
Step 1: 0 + 639 = 639
Step 2: 639 + 639 = 1278
Step 3: 1278 + 639 = 1917
Step 4: 1917 + 639 = 2556
Step 5: 2556 + 639 = 3195
Step 6: 3195 + 639 = 3834
Step 7: 3834 + 639 = 4473
Step 8: 4473 + 639 = 5112
Step 9: 5112 + 639 = 5751
Step 10: 5751 + 639 = 6390
Step 11: 6390 + 639 = 7029
Step 12: 7029 + 639 = 7668
Step 13: 7668 + 639 = 8307
Step 14: 8307 + 639 = 8946
Step 15: 8946 + 639 = 9585
Step 16: 9585 + 639 = 10224
Step 17: 10224 + 639 = 10863
Step 18: 10863 + 639 = 11502
Step 19: 11502 + 639 = 12141
Step 20: 12141 + 639 = 12780
Step 21: 12780 + 639 = 13419
Step 22: 13419 + 639 = 14058
Step 23: 14058 + 639 = 14697
Step 24: 14697 + 639 = 15336
Step 25: 15336 + 639 = 15975
Step 26: 15975 + 639 = 16614
Step 27: 16614 + 639 = 17253
Step 28: 17253 + 639 = 17892
Step 29: 17892 + 639 = 18531
Step 30: 18531 + 639 = 19170
Step 31: 19170 + 639 = 19809
Step 32: 19809 + 639 = 20448
Step 33: 20448 + 639 = 21087
Step 34: 21087 + 639 = 21726
Step 35: 21726 + 639 = 22365
Step 36: 22365 + 639 = 23004
Step 37: 23004 + 639 = 23643
Step 38: 23643 + 639 = 24282
Step 39: 24282 + 639 = 24921
Step 40: 24921 + 639 = 25560
Step 41: 25560 + 639 = 26199
Step 42: 26199 + 639 = 26838
Step 43: 26838 + 639 = 27477
Step 44: 27477 + 639 = 28116
Step 45: 28116 + 639 = 28755
Step 46: 28755 + 639 = 29394
Step 47: 29394 + 639 = 30033
Step 48: 30033 + 639 = 30672
Step 49: 30672 + 639 = 31311
Step 50: 31311 + 639 = 31950
Step 51: 31950 + 639 = 32589
Step 52: 32589 + 639 = 33228
Step 53: 33228 + 639 = 33867
Step 54: 33867 + 639 = 34506
Step 55: 34506 + 639 = 35145
Step 56: 35145 + 639 = 35784
Step 57: 35784 + 639 = 36423
Step 58: 36423 + 639 = 37062
Step 59: 37062 + 639 = 37701
Step 60: 37701 + 639 = 38340
Step 61: 38340 + 639 = 38979
Step 62: 38979 + 639 = 39618
Step 63: 39618 + 639 = 40257
Step 64: 40257 + 639 = 40896
Step 65: 40896 + 639 = 41535
Step 66: 41535 + 639 = 42174
Step 67: 42174 + 639 = 42813
Step 68: 42813 + 639 = 43452
Step 69: 43452 + 639 = 44091
Step 70: 44091 + 639 = 44730
Step 71: 44730 + 639 = 45369
Step 72: 45369 + 639 = 46008
Step 73: 46008 + 639 = 46647
Step 74: 46647 + 639 = 47286
Step 75: 47286 + 639 = 47925
Step 76: 47925 + 639 = 48564
Step 77: 48564 + 639 = 49203
Step 78: 49203 + 639 = 49842
Step 79: 49842 + 639 = 50481
Step 80: 50481 + 639 = 51120
Step 81: 51120 + 639 = 51759
Step 82: 51759 + 639 = 52398
Step 83: 52398 + 639 = 53037
Step 84: 53037 + 639 = 53676
Step 85: 53676 + 639 = 54315
Step 86: 54315 + 639 = 54954
Step 87: 54954 + 639 = 55593
Step 88: 55593 + 639 = 56232
Step 89: 56232 + 639 = 56871
Step 90: 56871 + 639 = 57510
Step 91: 57510 + 639 = 58149
Step 92: 58149 + 639 = 58788
Step 93: 58788 + 639 = 59427
Step 94: 59427 + 639 = 60066
Step 95: 60066 + 639 = 60705
Step 96: 60705 + 639 = 61344
Step 97: 61344 + 639 = 61983
Step 98: 61983 + 639 = 62622
Step 99: 62622 + 639 = 63261
Step 100: 63261 + 639 = 63900
Step 101: 63900 + 639 = 64539
Step 102: 64539 + 639 = 65178
Step 103: 65178 + 639 = 65817
Step 104: 65817 + 639 = 66456
Step 105: 66456 + 639 = 67095
Step 106: 67095 + 639 = 67734
Step 107: 67734 + 639 = 68373
Step 108: 68373 + 639 = 69012
Step 109: 69012 + 639 = 69651
Step 110: 69651 + 639 = 70290
Step 111: 70290 + 639 = 70929
Step 112: 70929 + 639 = 71568
Step 113: 71568 + 639 = 72207
Step 114: 72207 + 639 = 72846
Step 115: 72846 + 639 = 73485
Step 116: 73485 + 639 = 74124
Step 117: 74124 + 639 = 74763
Step 118: 74763 + 639 = 75402
Step 119: 75402 + 639 = 76041
Step 120: 76041 + 639 = 76680
Step 121: 76680 + 639 = 77319
Step 122: 77319 + 639 = 77958
Step 123: 77958 + 639 = 78597
Step 124: 78597 + 639 = 79236
Step 125: 79236 + 639 = 79875
Step 126: 79875 + 639 = 80514
Step 127: 80514 + 639 = 81153
Step 128: 81153 + 639 = 81792
Step 129: 81792 + 639 = 82431
Step 130: 82431 + 639 = 83070
Step 131: 83070 + 639 = 83709
Step 132: 83709 + 639 = 84348
Step 133: 84348 + 639 = 84987
Step 134: 84987 + 639 = 85626
Step 135: 85626 + 639 = 86265
Step 136: 86265 + 639 = 86904

So, 639*136 = 86904