Explanation:
Fgravity = G*(mass1*mass2)/D²
G is the gravitational constant throughout the universe.
D is the distance between both objects.
D is now reduced by a factor of 5, meaning Dnew = D/5 we get
Fgravitynew = G*(mass1*mass2)/(D/5)² =
= G*(mass1*mass2)/(D²/25) =
= 25* G*(mass1*mass2)/D² = 25* Fgravity
the new force of gravity/attraction is 25×16 = 400 units.