Gravitational Force: Tripling Distance - Factor 3 or 6?

[chuffman]

Homework Statement

If you triple the distance between two objects the gravitational force will...
A. Increase by the factor of 3
B. decrease by a factor of 3
C. Decrease by a factor of 6
D. Increase by a factor of 9
E. decrease by a factor of 9

Homework Equations

The Attempt at a Solution

Obviously it decreases but I'm just not sure I know what information I'm supposed to use to come to the right factor.

 

[TSny]

Newton's law of gravitation states that the force varies "inversely as the square of the distance".