Question

A circle with a radius of R is inscribed in a square. On the corner of the square are point charges of +q, +q, -q, and +q. On the circle are charges of +2q, +2q, -q, and +q. (See sketch.) If q = 4.8 micro-coulombs, and the total potential at the center of the circle due to all the charges on both the circle and the square is 2.5 x 103 V, what is the radius of the circle in meters?