Two large, parallel, conducting plates are 9.1 cm apart and have charges of equal magnitude and opposite sign on their facing surfaces. An electrostatic force of 4.2 x 10-15 N acts on an electron placed anywhere between the two plates. (Neglect fringing.) (a) Find the electric field (in N/C) at the position of the electron. (b) What is the potential difference in volts between the plates?