PLEASE HELP! The gravitational force that Earth exerts on an object is inversely proportional to the square of the distance between the center of the Earth and the object. When Bill is on the surface of Earth, 4,000 miles from the center, the gravitational force is 600 Newtons. What is the gravitational force (in Newtons) that the Earth exerts on him when he's standing on the moon, 240,000 miles from the center of the earth? Express your answer as a fraction

Inverse: Flipping the fraction of a number. For example the inverse of 2 would be 1/2. So force/1 has to = x/radius^2

Find "x":
 [tex] F_{gravity} = \frac{x}{r^2} [/tex]
Plug in numbers given:
 [tex] F_{gravity} = \frac{x}{r^2} [/tex]
[tex]600= \frac{x}{(4,000)^2} [/tex]
[tex]600= \frac{x}{16,000,000} [/tex]
[tex]x=9,600,000,000[/tex]

Find Force using x and the new radius:
 [tex] F_{gravity} = \frac{x}{r^2} [/tex]
 [tex] F_{gravity} = \frac{9,600,000,000}{(240,000)^2} [/tex] = 1/6