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 30. So, we're going to take the number 639 and add it to itself 30 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

So, 639*30 = 19170