OK, let's crack this. We're given 625 and our task is to multiply it by 4. Essentially, we'll be adding 625 to itself 4 times.
Step 1: 0 + 625 = 625
Step 2: 625 + 625 = 1250
Step 3: 1250 + 625 = 1875
Step 4: 1875 + 625 = 2500

So, 625*4 = 2500