OK, let's crack this. We're given 515 and our task is to multiply it by 15. Essentially, we'll be adding 515 to itself 15 times.
Step 1: 0 + 515 = 515
Step 2: 515 + 515 = 1030
Step 3: 1030 + 515 = 1545
Step 4: 1545 + 515 = 2060
Step 5: 2060 + 515 = 2575
Step 6: 2575 + 515 = 3090
Step 7: 3090 + 515 = 3605
Step 8: 3605 + 515 = 4120
Step 9: 4120 + 515 = 4635
Step 10: 4635 + 515 = 5150
Step 11: 5150 + 515 = 5665
Step 12: 5665 + 515 = 6180
Step 13: 6180 + 515 = 6695
Step 14: 6695 + 515 = 7210
Step 15: 7210 + 515 = 7725

So, 515*15 = 7725