Let's roll up our sleeves and solve this. We have 644 and we're going to multiply it by 3, essentially adding 644 to itself 3 times.
Step 1: 0 + 644 = 644
Step 2: 644 + 644 = 1288
Step 3: 1288 + 644 = 1932

So, 644*3 = 1932