Coulomb's Law Problems

Two metal spheres are charged, q$_1$ = 6Q and q$_2$ = -2Q, and are separated by a distance d. The attractive force between these two spheres is 20 N. The metal spheres are then brought together so they are touching, and then separated again a distance d. What is the new charge on the metal spheres and what is the new force between them?

Two objects, whose charges are +3 nC and -2 nC, are separated by 1.0 mm. Find the magnitude of the attractive force that either charge exerts on the other.

In the figure below, L = 1.0 mm, q$_1$ = +3 nC, q$_2$ = -2 nC, and q$_3$ is +4 nC. Find the magnitude and direction of the net electrostatic force on q$_3$

In the figure below, A = 3 cm, B = 1 cm, q$_1$ = +15 nC, q$_2$ = -5 nC, and q$_3$ is -10 nC. Find the magnitude and direction of the net electrostatic force on q$_3$