$2\mathrm{.}37$ A U$-$tube manometer is connected to a closed tank containing air and water as shown in Fig. P$2\mathrm{.}37.$ At the closed end of the manometer the air pressure is $16$ psia. Determine the reading on the pressure gage for a differential reading of $4ft$ on the manometer. Express your answer in psi $($gage$).$ Assume standard atmospheric pressure and neglect the weight of the air columns in the manometer.