A plastic rod has been bent into a circle of radius R = 6.90 cm. It has a charge Q1 = +2.66 pC uniformly distributed along one-quarter of its circumference and a charge Q2 = -6Q1 uniformly distributed along the rest of the circumference (see the figure). With V = 0 at infinity, what is the electric potential (a) at the center C of the circle and (b) at point P, which is on the central axis of the circle at distance D = 3.46 cm from the center? D Q2 R C 21 (a) Number Units (b) Number i Units