I am stuck on these physics problems please help!?

Question

On Apollo missions to the Moon, the command module orbited at an altitude of 157 km above the lunar surface. How long did it take for the command module to complete one orbit?
h

A typical GPS (Global Positioning System) satellite orbits at an altitude of 4.1 107 m.
a) Find the orbital period of such a satellite.
hours
(b) Find the orbital speed of such a satellite.
km/s

An astronaut exploring a distant solar system lands on an unnamed planet with a radius of 2550 km. When the astronaut jumps upward with an initial speed of 3.51 m/s, she rises to a height of 0.72 m. What is the mass of the planet?
kg

Answer 1

use v^2 = GM/r

v = root GM/2r

orbit = 2 pi r

for part 2 use suvat equations, s=vu+.5at^2 etc and it should fall out

Answer 2

v = sqrt(gR)