Six point charges, each a value of Q, are situated at (d, 0, 0), (-d, 0, 0), (0, d, 0),
(0, -d, 0), (0, 0, d), and (0, 0, -d). A test charge q located at the origin is displaced by a distance l << d along the positive x-axis. Find an approximate expression for the electric force acting on the charge.