Monatomic Gas Calculating temperature and pressure

Perform the calculations below :i) Monatomic gas where Cv,m=3R/2,A bottle at 285 K contains an ideal gas at a pressure of 155.7103 Pa. The rubber stopper closing the bottle is removed. The gas expands adiabatically against and external pressure of Pext=111.4103 Pa, and some gas is expe