Help with gravitation problem for physics please?

As an astronaut, you observe a small planet to be spherical. After landing on the planet, you set off, walking always straight ahead, and find yourself returning to your spacecraft from the opposite side after completing a lap of 25.7 km. You hold a hammer and a falcon feather at a height of 1.36 m, release them, and observe that they fall together to the surface in 28.7 s. Determine the m of the planet.