Think of it as four groups of four plus another four groups of four . Then add four more to the sum. Then take away four groups of four . Always multiply before adding or subtracting. Multiply the numbers which are "touching" the X. So, four groups of four are sixteen and the other four groups of four are also sixteen. Sixteen plus sixteen is thirty-two. When you add four more, you'll have thirty-six. Now we'll take away the other four groups of four (sixteen). What is thirty-six minus sixteen? Twenty, right? I always like to take think of equations in concrete terms and talk it out to myself to really comprehend the idea. Hope this helps.