A star near the visible edge of a galaxy travels in a uniform circular orbit. It is 41,500 ly (light-years) from the galactic center and has a speed of 275 km/s.

1. Estimate the total mass of the galaxy based on the motion of the star. Gravitational constant is 6.67410¹¹ m³/(kgs²) and mass of the Sun M_s=1.9910³⁰kg. _____billion solar mass

2. The total visible mass (i.e., matter we can detect via electromagnetic radiation) of the galaxy is 10¹¹ solar masses. What fraction of the total mass of the galaxy is visible, according to this estimate?