Physics 3. (10 points) Find the E field a distance z above the center of a cube, where a point charge +q is placed at each corner of the top face (positive z) and -q on the bottom face (negative z). Assume the distance from the center to a corner is a known length a. After computing the full result, find the leading z-dependence of E far away from the cube, i.e. when a/z - 0