Mars has a mass of about 6.4*10^23 kg, and it's moon Phobos has a mass of about 9.6*10^15 kg.If the magnitude of the grvitational force between the two bodies is 4.6* 10^15 N, how far apart are Mars and Phobos?

Answer 1

It is simple algebra:

Fg= G M1*M2/distance^2

solve for distance