Electrical potential of a non uniformly charged ring?

A plastic rod has been bent into a circle of radius R = 10.6 cm. It has a charge Q1 = +7.06 pC uniformly distributed along one-quarter of its circumference and a charge Q2 = -6Q1 uniformly distributed along the rest of the circumference (Fig. 24-37). With V = 0 at infinity, what is the electric potential in volts (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 = 5.79 cm from the center?