A positive point charge is surrounded by an equipotential surface A, which has a radius of rA. A positive test charge moves from surface A to another equipotential surface B, which has a radius rB. In the process, the electric force does negative work.
The positive point charge is q = +7.5 10-8 C, and the test charge is q0 = +6.0 10-11 C. The work done by the electric force as the test charge moves from surface A to surface B is WAB = -8.1 10-9 J. The radius of surface A is rA = 1.7 m.
Find rB, the radius of surface B.
Could someone help me set this problem up. I hit a wall and don't know what to do