A giant air filled capacitor with 122

A giant air filled capacitor with 122.22 (F) with charge 0.039 (C) on its plates of area 144 (m2) is attached to a spring stiffness 22.5 (N/m), and the left-hand plate oscillates without friction horizontally as shown in the diagram. The right-hand plate is fixed in place. The left-hand plate is pulled to the right so that it stretches the spring a distance 13.392 (m) and then let go. If the variable x is the displacement of the left-hand plate from its equilibrium position (xequ), what is the force on the charge on the fixed plate in N?

(Assume the plates are large compared to their separation and give answers to at least 3 sig figs).