The formula that we wil be using is the formula for two charges q and Q separated by a distance r which is: U = kQq/r Where: U = electric potential, Q and q = point charges, and r = the distance between the point charges. So we are looking for 'r', rearranging the formula would give us: U*r = kQq r = kQq/U -> this will be the formula that we will be using. r = (9 x 10^9)*(7.22 x 10^-6)*(-32.5 x 10^-6) / -117 r = .01805 m