Two charged spheres are held a distance, r, apart. One sphere has a charge of +4µC, and the other sphere has a charge of +8µC. Compare the force of the +4µC sphere on the +8µC sphere with the force of the +8µC sphere on the +4µC sphere.
Coulomb's law gives us the equation for finding the electrostatic force between two stationary point charges. The equation is shown below:
F = K * (q1*q2)/r^2
F is the electrostatic force between the two charges, K is Coulomb's constant, q1 and q2 are the magnitude of the two charges, and r is the distance between them. If the two charges have the same sign, the force between the two will be repulsive. If the two charges have different signs, the force between them will be attractive.
In your case, both charges are positive, thus the electrostatic charge between them will be repulsive. The +8 microC charge will exert a force on the +4 microC and vice versa. This means that the magnitude of these two forces is the same but in the opposite directions (the forces have a 180 degree angle between them).