Answer: The force is 6.25 times stronger.
Explanation:
The formula to find the force of attraction between any two object is given by :-
(i)
, where M and m are the masses of the objects , d is the distance between them and G is gravitational constant.
If you decrease the distance between two celestial objects by a factor of 2.5, then , the new distance will become

Plug this in the above formula , we get

Hence, the force is 6.25 times stronger.