"9. If a is a non-zero constant, determine the vertex of the function y = -x2 + 4ax + 3 in terms of a. A) (2a, 4a2 + 3) B) (-2a, 12a2 + 3) C) (a, 3a2 + 3) D) (-a, -5a2 + 3) E) None of these