Thanks a lot Patrick, my Physics teacher was out sick today, but if it is impossible to calculate the rest of the mass of the Milky Way using Kepler's third law then I guess the answer that I got, assuming that it is right, is what my teacher was looking for.
I have one more question though...
The typed question and attempt at it are below:
Question:
The Sun orbits the black hole in the center of the Milky Way galaxy. It takes approximately 225 million years for the sun to make one revolution, and the sun is approximately 26,000 light-years away. Using this information and...