OK, let's work through this together. We're starting with 641 and we're going to multiply it by 5, which means we add 641 to itself 5 times.
Step 1: 0 + 641 = 641
Step 2: 641 + 641 = 1282
Step 3: 1282 + 641 = 1923
Step 4: 1923 + 641 = 2564
Step 5: 2564 + 641 = 3205

So, 641*5 = 3205