Keep in mind that you need to use the distance from the center of the earth, so add the height above the surface to the radius of the earth. Note that the diameter is given in the problem, so you need to calculate the radius.
What is the ratio of the gravitational force on an astronaut when he is in a space satellite in a circular orbit 300 km above the earth to the gravitational force on the astronaut when he is on the surface of the earth? The earth's diameter is 12,760 km.