Question

Three concentric rings and one point charge are in the same plane as shown in the above diagram. The linear charge densities of the rings are ë1 = 2.60nC/m, ë2 = -1.10nC/m, and ë3 = 2.20nC/m with corresponding radii of r1 = 86.0cm, r2 = 64.0cm, and r3 = 46.0cm. The point charge at the center of the rings has a net charge of q = -3.10nC. What is the magnitude of the electric field at a point along the axis that runs through the center of the rings, which is a distance a = 2.40m away from the center of the rings?