OK, let's work through this together. We're starting with 784 and we're going to multiply it by 3, which means we add 784 to itself 3 times.
Step 1: 0 + 784 = 784
Step 2: 784 + 784 = 1568
Step 3: 1568 + 784 = 2352

So, 784*3 = 2352