a rectangular box with edges located at (0,0,0); (a,0,0); (0,b,0) and (0,0,c) is half-filled from z=0 up to z=c/2 with a dielectric with constsnt e. the top half is empty. the cover at z=c is maintained at the constant potentialf0, and the other five sides are grounded. find f(x) inside the box