OK, let's crack this. We're given 400 and our task is to multiply it by 12. Essentially, we'll be adding 400 to itself 12 times.
Step 1: 0 + 400 = 400
Step 2: 400 + 400 = 800
Step 3: 800 + 400 = 1200
Step 4: 1200 + 400 = 1600
Step 5: 1600 + 400 = 2000
Step 6: 2000 + 400 = 2400
Step 7: 2400 + 400 = 2800
Step 8: 2800 + 400 = 3200
Step 9: 3200 + 400 = 3600
Step 10: 3600 + 400 = 4000
Step 11: 4000 + 400 = 4400
Step 12: 4400 + 400 = 4800

So, 400*12 = 4800