A force of gravity exists between two masses. How is the initial force of gravity (F1) affected if the separation distance between them is modified in the following ways to yield a new force of gravity (F2)?
(a) The separation distance is doubled (i.e. increased by a factor of 2).
F2 / F1 = ?

(b) The separation distance is decreased to one-fourth of the original length.
F2 / F1 = ?

Newton's law of gravity:

F = GMM'/R^2

F=Force of attraction between two bodies
G= Gravitational Constant
M= Mass of one body
M' = Mass of other body
R = Distance between the two bodies