Carlos did not use order of operations. The order of operations goes first you do Parentheses, Exponents, Multiplication, Division, Addition, Subtraction. First you do the parentheses which is 2 x 6 so now your equation is 20 - 12 + 8 / 4. Since you don't have any exponents nor multiplication left you move onto divison which is 8 / 4. Know your equation is 20 - 12 + 2. You do addtion which is 12 + 2. Then you do subtraction 20 - 14 which equals 6.
Hope this helps :)