A long, thin rod (length = 3.0 m) lies along the x axis, with its midpoint at the origin. In a vacuum, a +8.0C point charge is fixed to one end of the rod, and a -8.0C point charge is fixed to the other end. Everywhere in the x, y plane there is a constant external electric field (magnitude 7.0 × 103 N/C) that is perpendicular to the rod. With respect to the z axis, find the magnitude of the net torque applied to the rod.