OK, let's crack this. We're given 665 and our task is to multiply it by 20. Essentially, we'll be adding 665 to itself 20 times.
Step 1: 0 + 665 = 665
Step 2: 665 + 665 = 1330
Step 3: 1330 + 665 = 1995
Step 4: 1995 + 665 = 2660
Step 5: 2660 + 665 = 3325
Step 6: 3325 + 665 = 3990
Step 7: 3990 + 665 = 4655
Step 8: 4655 + 665 = 5320
Step 9: 5320 + 665 = 5985
Step 10: 5985 + 665 = 6650
Step 11: 6650 + 665 = 7315
Step 12: 7315 + 665 = 7980
Step 13: 7980 + 665 = 8645
Step 14: 8645 + 665 = 9310
Step 15: 9310 + 665 = 9975
Step 16: 9975 + 665 = 10640
Step 17: 10640 + 665 = 11305
Step 18: 11305 + 665 = 11970
Step 19: 11970 + 665 = 12635
Step 20: 12635 + 665 = 13300

So, 665*20 = 13300