Answer
Doubling both of the charges means the force is multiplied by 4 compared to its original value, no matter the sign of the original charges. Coulomb’s law defends our answer.
Work Step by Step
Use Coulomb's Law.
$$F = k \frac{q_{1} \; q_{2}}{d^{2}}$$
If both charges are doubled, the force is quadrupled.
This statement does not depend on the original value or signs of the charges q.
