The answer is B.
The reason behind it being that since the sides of the entire patio are given, you can multiply them and get the area of the entire patio, then you can subtract the area of the bench, which in this case is 12 because 2 times 6 is 12. Since you can’t solve for (x+20) or (x+10), you can multiply them by themselves. This would give you the equation (x+20)(x+10)-12.
