Without delay, let's solve this. We've got 20 and we will be multiplying it by 4, that is, adding 20 to itself 4 times.
Step 1: 0 + 20 = 20
Step 2: 20 + 20 = 40
Step 3: 40 + 20 = 60
Step 4: 60 + 20 = 80

So, 20*4 = 80