OK, let's work through this together. We're starting with 612 and we're going to multiply it by 15, which means we add 612 to itself 15 times.
Step 1: 0 + 612 = 612
Step 2: 612 + 612 = 1224
Step 3: 1224 + 612 = 1836
Step 4: 1836 + 612 = 2448
Step 5: 2448 + 612 = 3060
Step 6: 3060 + 612 = 3672
Step 7: 3672 + 612 = 4284
Step 8: 4284 + 612 = 4896
Step 9: 4896 + 612 = 5508
Step 10: 5508 + 612 = 6120
Step 11: 6120 + 612 = 6732
Step 12: 6732 + 612 = 7344
Step 13: 7344 + 612 = 7956
Step 14: 7956 + 612 = 8568
Step 15: 8568 + 612 = 9180

So, 612*15 = 9180