If f(x) = 2x - 6 and g(x) = 3x + 9, find (f + g)(x).
O A. (f+ g)(x) = x+15
O B. (f+ g)(x) = 5x + 3
O C. (f+ g)(x) = -x - 15
O D. (f+ g)(x) = 5x + 15