Your answer is A, -3.
I’m not sure if you have studied the factor theorem yet, but the factor theorem states that if you have a function f(x), and f(3) = 0, that is, when you substitute 3 into the function you get 0, then (x - 3) must be a factor of the function.
This means that you can see that (x - 1) perfectly factors into the function, and so does (x + 3), because both of their remainders are 0. Therefore, we know that x = 1 and x = -3 are both roots, and since 1 isn’t a given option, your answer is -3.
I hope this helps! Let me know if you have any questions :)