Let's roll up our sleeves and solve this. We have 636 and we're going to multiply it by 4, essentially adding 636 to itself 4 times.
Step 1: 0 + 636 = 636
Step 2: 636 + 636 = 1272
Step 3: 1272 + 636 = 1908
Step 4: 1908 + 636 = 2544

So, 636*4 = 2544