Eight charges are placed at the eight corners of a cube at a distance of 0.1 m away from the cube's center. The top surface of the cube has charges that are positive and equal to 10-7 C. The remaining charges are negative and equal to -2×10-7C. The potential at infinity is defined to be 0. a) What is the electrostatic potential at the center of the square? b) The negative charges are moved to infinity. What is the potential energy of the system now?