Let's get this math done. We have 720 and we're going to multiply it by 15. This is the same as taking 720 and adding it to itself 15 times.
Step 1: 0 + 720 = 720
Step 2: 720 + 720 = 1440
Step 3: 1440 + 720 = 2160
Step 4: 2160 + 720 = 2880
Step 5: 2880 + 720 = 3600
Step 6: 3600 + 720 = 4320
Step 7: 4320 + 720 = 5040
Step 8: 5040 + 720 = 5760
Step 9: 5760 + 720 = 6480
Step 10: 6480 + 720 = 7200
Step 11: 7200 + 720 = 7920
Step 12: 7920 + 720 = 8640
Step 13: 8640 + 720 = 9360
Step 14: 9360 + 720 = 10080
Step 15: 10080 + 720 = 10800

So, 720*15 = 10800