If a Spherical Galaxy of Diameter 100,000 Ly Contained Enough

Multiple Choice

If a spherical galaxy of diameter 100,000 ly contained enough mass to be a black hole, what would be its mass?

A) 200 x 10⁹ kg
B) 400 x 10⁹ kg
C) 6.9 x 10²³ kg
D) 3.2 x 10⁴⁷ kg
E) 6.4 x 10⁴⁷ kg