Alright, let's solve this math problem step by step. First, we have the number 123. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 15. So, we're going to take the number 123 and add it to itself 15 times.
Step 1: 0 + 123 = 123
Step 2: 123 + 123 = 246
Step 3: 246 + 123 = 369
Step 4: 369 + 123 = 492
Step 5: 492 + 123 = 615
Step 6: 615 + 123 = 738
Step 7: 738 + 123 = 861
Step 8: 861 + 123 = 984
Step 9: 984 + 123 = 1107
Step 10: 1107 + 123 = 1230
Step 11: 1230 + 123 = 1353
Step 12: 1353 + 123 = 1476
Step 13: 1476 + 123 = 1599
Step 14: 1599 + 123 = 1722
Step 15: 1722 + 123 = 1845

So, 123*15 = 1845