OK, let's work through this together. We're starting with 609 and we're going to multiply it by 15, which means we add 609 to itself 15 times.
Step 1: 0 + 609 = 609
Step 2: 609 + 609 = 1218
Step 3: 1218 + 609 = 1827
Step 4: 1827 + 609 = 2436
Step 5: 2436 + 609 = 3045
Step 6: 3045 + 609 = 3654
Step 7: 3654 + 609 = 4263
Step 8: 4263 + 609 = 4872
Step 9: 4872 + 609 = 5481
Step 10: 5481 + 609 = 6090
Step 11: 6090 + 609 = 6699
Step 12: 6699 + 609 = 7308
Step 13: 7308 + 609 = 7917
Step 14: 7917 + 609 = 8526
Step 15: 8526 + 609 = 9135

So, 609*15 = 9135