The arm in Coulomb's torsion balance was a rod with a charged ball at one end and a counterweight on the other. Suppose that the length of the arm in such a balance is 12cm. Suppose that the probe is at a distance of 2.6cm in a direction perpendicular to the arm. If the charged ball and the probe both carry 1.5 x 10^-9 C, what is the torque exerted on the balance arm?