The Orbits of a Few Dozen Stars Have Been Carefully

The orbits of a few dozen stars have been carefully monitored over a few decades in the proximity of the supermassive black hole at the center of the Milky Way (see the figure shown below) .One example is the so-called star SO-1, whose semimajor axis is 3,300 AU long and has a period of 94.1 years.What is the estimated mass of the central supermassive black hole?

A) 3.4 *10⁶ M_SUN
B) 7.6 * 10⁹ M_SUN
C) 1.5 * 10⁸ M_SUN
D) 4.0 * 10⁶ M_SUN
E) 3.4* 10¹¹ M_SUN