Suppose That Scientists in the Future Are Able to Observe

Suppose that scientists in the future are able to observe a star orbiting the central region of the Andromeda Galaxy and find that it has an orbital period of 31 years and a semimajor axis of 4,500 AU.The mass of Andromeda's central black hole must then be around

A) 4.0 * 10⁶ M_SUN
B) 9.5 *10⁶ M_SUN
C) 4.0 * 10⁷ M_SUN
D) 9.5 * 10⁷ M_SUN
E) 4.0 * 10⁸ M_SUN