A parallel$-$plate air$-$filled capacitor having area $39$ cm$2$ and plate spacing $1\mathrm{.}5$ mm is charged to a potential difference of $890$ V$.$ Find $($a$)$ the capacitance, $($b$)$ the magnitude of the charge on each plate, $($c$)$ the stored energy, $($d$)$ the electric field between the plates, $($e$)$ the energy density between the plates.