Let's roll up our sleeves and solve this. We have 45 and we're going to multiply it by 12, essentially adding 45 to itself 12 times.
Step 1: 0 + 45 = 45
Step 2: 45 + 45 = 90
Step 3: 90 + 45 = 135
Step 4: 135 + 45 = 180
Step 5: 180 + 45 = 225
Step 6: 225 + 45 = 270
Step 7: 270 + 45 = 315
Step 8: 315 + 45 = 360
Step 9: 360 + 45 = 405
Step 10: 405 + 45 = 450
Step 11: 450 + 45 = 495
Step 12: 495 + 45 = 540

So, 45*12 = 540