A thin, square, conducting plate 45.0-cm on a side lies in the xy plane. A total charge of 0.0680 is placed on the plate. Find
(A) the charge density on the plate, and
(B) the electric field Ez just above the plate. Assume the charge density is uniform and that "up" is the positve direction. [(A) nC/m^2] [(B) N/C]