OK, let's crack this. We're given 125 and our task is to multiply it by 15. Essentially, we'll be adding 125 to itself 15 times.
Step 1: 0 + 125 = 125
Step 2: 125 + 125 = 250
Step 3: 250 + 125 = 375
Step 4: 375 + 125 = 500
Step 5: 500 + 125 = 625
Step 6: 625 + 125 = 750
Step 7: 750 + 125 = 875
Step 8: 875 + 125 = 1000
Step 9: 1000 + 125 = 1125
Step 10: 1125 + 125 = 1250
Step 11: 1250 + 125 = 1375
Step 12: 1375 + 125 = 1500
Step 13: 1500 + 125 = 1625
Step 14: 1625 + 125 = 1750
Step 15: 1750 + 125 = 1875

So, 125*15 = 1875