On the surface of planet Y, which has a mass of 4.83 x 10^24 kg, an object has a weight of 50 N and a mass of 30 kg. What is the radius of the planet?
a. 3.2 x 10^6 m
b. 4.2 x 10^6 m
c. 5.6 x 10^6 m
d. 6.8 x 10^6 m