posted by Gina .
Two newly discovered planets follow circular orbits around a star in a distant part of the galaxy. The orbital speeds of the planets are determined to be 41.3 km/s and 52.7 km/s. The slower planet's orbital period is 7.74 years. (a) What is the mass of the star? (b) What is the orbital period of the faster planet, in years?
i used v=2pi(radius)/T to find the radius, and converted the km to m and the years to seconds, but how do i get the mass from this?