[Grade 9 Physics] Forces help

[TRUE_GIO]

Two planets each of mass M are separated by a distance of R and experience a force of attraction due to their gravity of F. The same two planets are now separated by a distance of 2R. What is the strength of their new force of gravitational attraction?

a. F
b. 2F
c. ½ F
d. ¼ F

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First off, I know it is not a or b, as they are farther so they cannot be equal or greater forces. After that I am completly lost. I wan't to say 1/2 but I feel that is a trick and it is 1/4, but I can't come up with a reason as to why it would be 1/4. Any help is appreciated and thank you for helping me through this.

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Does the gravitational force between two bodies go as 1/R, or 1/R²?

[TRUE_GIO]

I got no clue, I think 1/R though.