OK, let's work through this together. We're starting with 813 and we're going to multiply it by 5, which means we add 813 to itself 5 times.
Step 1: 0 + 813 = 813
Step 2: 813 + 813 = 1626
Step 3: 1626 + 813 = 2439
Step 4: 2439 + 813 = 3252
Step 5: 3252 + 813 = 4065

So, 813*5 = 4065