Gravitational field strength of 0

[inuyasha555]

Homework Statement

A planet of mass 1.88x10^21 kg has a moon of mass 4.56^10^19 kg. The distance between their centers is 3.94x10^8 m. How far from the center of the planet (along the line joining the planet and the moon) is the net gravitational field strength, due to the two bodies, equal to 0?

Homework Equations

Fg = GMm/r^2

The Attempt at a Solution

GMm/r^2 - GMm/r^2 = 0.

Somewhere in there I'm thinking I can put in the point (x) but I have no idea where or how to approach this.

 

[rl.bhat]

If d is the distance between the planet and the moon, and the x is the distance at which the field is zero from the planet, then the distance from the moon to that point is (d - x).