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 55. So, we're going to take the number 639 and add it to itself 55 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

So, 639*55 = 35145