This is just a simple factoring problem, and although it is in the calculator section of the SAT, you don’t even need a calculator to solve this problem. If we want to factor x^2+9x-36 into (x+a)(x+b) we can find what two numbers add up to 9 and also multiply to get -36. 6 + 3 could work to get 9, but they don’t multiply to get -36. Since -36 is a negative number we know that one of the numbers must be positive, and the other must be negative. The numbers 12 and -3 work, because when they are multiplied together, you get -36, and when you add them, you get 9. If we plug those numbers into the equation, we get (x + 12)(x – 3), and since 12 is an option for an answer and -3 isn’t, the answer must be D.