Let's roll up our sleeves and solve this. We have 635 and we're going to multiply it by 15, essentially adding 635 to itself 15 times.
Step 1: 0 + 635 = 635
Step 2: 635 + 635 = 1270
Step 3: 1270 + 635 = 1905
Step 4: 1905 + 635 = 2540
Step 5: 2540 + 635 = 3175
Step 6: 3175 + 635 = 3810
Step 7: 3810 + 635 = 4445
Step 8: 4445 + 635 = 5080
Step 9: 5080 + 635 = 5715
Step 10: 5715 + 635 = 6350
Step 11: 6350 + 635 = 6985
Step 12: 6985 + 635 = 7620
Step 13: 7620 + 635 = 8255
Step 14: 8255 + 635 = 8890
Step 15: 8890 + 635 = 9525

So, 635*15 = 9525