The Sun rotates about the center of the Milky Way Galaxy at a distance of about 3.00x10^4 light years from the center (1ly= 9.50x10^5 m). If it takes about 200 million years to make one rotation, estimate the mass of our galaxy. Assume the mass distribution of our galaxy is concentrated mostly in a central uniform sphere. If all the stars had about the same mass as our Sun, how many stars would there be in our galaxy?
I have no clue, the most common equation I use is g=GM/r^2 and a=v^2/r.
The Attempt at a Solution
I do not know where to start.