OK, let's work through this together. We're starting with 638 and we're going to multiply it by 3, which means we add 638 to itself 3 times.
Step 1: 0 + 638 = 638
Step 2: 638 + 638 = 1276
Step 3: 1276 + 638 = 1914

So, 638*3 = 1914