Please help! I've tried several times on my calculator and I can't get it right!

Find the force of attraction on a 3 kg mass at the surface of a planet given the following information about the planet: mass = 5.98 x 1024 kg, radius = 6.38 x 106 m.

Find the force if the radius is doubled to 12.76 x 106m

duplicate question ; answered by Damon