Let's get this math done. We have 707 and we're going to multiply it by 15. This is the same as taking 707 and adding it to itself 15 times.
Step 1: 0 + 707 = 707
Step 2: 707 + 707 = 1414
Step 3: 1414 + 707 = 2121
Step 4: 2121 + 707 = 2828
Step 5: 2828 + 707 = 3535
Step 6: 3535 + 707 = 4242
Step 7: 4242 + 707 = 4949
Step 8: 4949 + 707 = 5656
Step 9: 5656 + 707 = 6363
Step 10: 6363 + 707 = 7070
Step 11: 7070 + 707 = 7777
Step 12: 7777 + 707 = 8484
Step 13: 8484 + 707 = 9191
Step 14: 9191 + 707 = 9898
Step 15: 9898 + 707 = 10605

So, 707*15 = 10605