OK, let's work through this together. We're starting with 879 and we're going to multiply it by 4, which means we add 879 to itself 4 times.
Step 1: 0 + 879 = 879
Step 2: 879 + 879 = 1758
Step 3: 1758 + 879 = 2637
Step 4: 2637 + 879 = 3516

So, 879*4 = 3516