Finding the mass of a sphere with uniform charge density

[ghost34]

Homework Statement

The sphere has radius R, and uniform volume charge density P. This sphere remains stationary (levitates) when placed above an infinite sheet of paper with a uniform surface charge density u. What is this sphere's mass?

Homework Equations

4/3 pi R^3 is the volume of a sphere
F=ma

The Attempt at a Solution

The only connection between mass and the charged situation I can see is with the Force=ma law, but as there isn't any acceleration, I can't figure out how to solve for m...any help would be appreciated, thanks

 

[Saitama]

To remain stationary, the net force on the ball should be zero. What are the forces acting on the ball?