A rigid tank contains 20 lbm of air at 20 psia and 70°F. More air is added to the tank until the pressure and temperature rise to 35 psia and 90°F, respectively. Determine the amount of air added to the tank.

A manometer is used to measure the pressure in a tank. The fluid used has a specific gravity of 0.85, and
the manometer column height is 55 cm. If the local atmospheric pressure is 96 kPa, determine the
absolute pressure within the tank.