The answer is -1. Due to PEMDAS, you have to do whatever is inside the parentheses first. When you replace “a” and “b” in the parentheses, it will give you 1+3 which is 4. After this, you have to do 4-6 in order to get -2. Then, you have to replace 2 in the denominator. By this point, it would be -2/2, which simplified to -1.