Let's roll up our sleeves and solve this. We have 84 and we're going to multiply it by 4, essentially adding 84 to itself 4 times.
Step 1: 0 + 84 = 84
Step 2: 84 + 84 = 168
Step 3: 168 + 84 = 252
Step 4: 252 + 84 = 336

So, 84*4 = 336