OK, let's crack this. We're given 4 and our task is to multiply it by 5. Essentially, we'll be adding 4 to itself 5 times.
Step 1: 0 + 4 = 4
Step 2: 4 + 4 = 8
Step 3: 8 + 4 = 12
Step 4: 12 + 4 = 16
Step 5: 16 + 4 = 20

So, 4*5 = 20