Asmall plastic sphere with a charge of -7.5 nc is near another small plastic sphere
with a charge of +11 nc. if the force between the spheres has a magnitude of 8.8×104
n, what is the distance between the spheres? what kind of force is this?

This force is called an electrostatic force. To solve for the value of the electrostatic force. Using Coulumbs Law: 

F = k * abs (Q1 * Q2) / r^2
where:
k = coulumb's constant, 8.988x10^9 N *m^2/ C^2
Q1 = first charge
Q2 = second charge
r = distance between charges

8.8x10^4 = 8.988x10^9 * abs((-7.5x10^-9) * (11x10^-9)) / r^2

solve for r