If both masses are increased by 60% and the distance between them is halved, by what percent will the force of attraction increase?
just plug in the new values:
F = GMm/d^2
new force
F' = G(1.6m)(1.6M)/(d/2)^2
= GmM/d^2 * 1.6^2 * 2^2
= 10.24F
I assume you can convert that to a percentage