OK, let's crack this. We're given 810 and our task is to multiply it by 4. Essentially, we'll be adding 810 to itself 4 times.
Step 1: 0 + 810 = 810
Step 2: 810 + 810 = 1620
Step 3: 1620 + 810 = 2430
Step 4: 2430 + 810 = 3240

So, 810*4 = 3240