OK, let's crack this. We're given 504 and our task is to multiply it by 3. Essentially, we'll be adding 504 to itself 3 times.
Step 1: 0 + 504 = 504
Step 2: 504 + 504 = 1008
Step 3: 1008 + 504 = 1512

So, 504*3 = 1512