The Sun, which is 2.2 x 1020 m from the center of the Milky Way galaxy, revolves around that center once every 2.5 X 108 years. Assuming each star in the Galaxy has a mass equal to the Sun's mass of 2.0 x 1030 kg, the stars are distributed uniformly in a sphere about the galactic center, and the Sun is at the edge of that sphere, estimate the number of stars in the Galaxy.