Let's roll up our sleeves and solve this. We have 864 and we're going to multiply it by 3, essentially adding 864 to itself 3 times.
Step 1: 0 + 864 = 864
Step 2: 864 + 864 = 1728
Step 3: 1728 + 864 = 2592

So, 864*3 = 2592