OK, let's work through this together. We're starting with 873 and we're going to multiply it by 3, which means we add 873 to itself 3 times.
Step 1: 0 + 873 = 873
Step 2: 873 + 873 = 1746
Step 3: 1746 + 873 = 2619

So, 873*3 = 2619