Let's roll up our sleeves and solve this. We have 780 and we're going to multiply it by 4, essentially adding 780 to itself 4 times.
Step 1: 0 + 780 = 780
Step 2: 780 + 780 = 1560
Step 3: 1560 + 780 = 2340
Step 4: 2340 + 780 = 3120

So, 780*4 = 3120