OK, let's work through this together. We're starting with 637 and we're going to multiply it by 4, which means we add 637 to itself 4 times.
Step 1: 0 + 637 = 637
Step 2: 637 + 637 = 1274
Step 3: 1274 + 637 = 1911
Step 4: 1911 + 637 = 2548

So, 637*4 = 2548