Let's roll up our sleeves and solve this. We have 641 and we're going to multiply it by 3, essentially adding 641 to itself 3 times.
Step 1: 0 + 641 = 641
Step 2: 641 + 641 = 1282
Step 3: 1282 + 641 = 1923

So, 641*3 = 1923