Apositive point charge (q = +8.54 x 10-8 c) is surrounded by an equipotential surface a, which has a radius of ra = 2.98 m. a positive test charge (q0 = +4.62 x 10-11 c) moves from surface a to another equipotential surface b, which has a radius rb. the work done by the electric force as the test charge moves from surface a to surface b is wab = -8.03 x 10-9 j. find rb.