Answer:
(1/4)F
Step-by-step explanation:
Let F be the force on charges q and q' separated by a distance, d
F = kqq'/d²
Now, if q and q' are doubled, our new charges are 2q and 2q' respectively and, if the distnace is increased by four times, then our new distance is 4d. So our new force F' = k (2q)(2q')/(4d)²
= 4kqq'/16d²
= kqq'/4d²
= F/4
So, the magnitude of our new force is F/4