If we take the zero reference for potential at infinity, find the potential at (0, 0, 2) caused by this charge configuration in free space (a) 12 nC/m on the line rho = 2.5 m, z = 0; (b) point charge of 18 nC at (1, 2, −1); (c) 12 nC/m on the line y = 2.5, z = 0, −1.0 < x < 1.0