Distance, masses.?

Question

Deimos orbits mars at a distance of 23,000km with a period of 1.3 days. Charon is estimated to orbit Pluto at about the same distance but with a period of 6.5 days. Use this information to compare the masses of Pluto and Mars.

Answer 1

Nah, I don't feel like comparing the masses of Pluto and Mars today. I'm more inclined to answer genuine questions.

Answer 2

Suppose one has 5x the mass of the other.

Answer 3

Equate gravitational attraction with centrifugal force. assume in both cases that the mass of the satellite is small compared with the mass of the "planet".  Calculate the period in terms of G, r, and planetary mass.  Compare the results for Pluto and Mars, and the ratio of masses should just fall out.