Air added to rigid tank 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 26.5 psia and 90°F, respectively. Determine the amount of air added to the tank. The gas constant of air is R= 0.3704 psia ft3/lbm-R The amount of airsibm.