Two moles of an ideal gas are contained under 50 atm and 300K. After remove the stopper 1, the gas expands adiabatically to stopper 2. The external pressure is 10 atm during expansion. The final pressure of the gas is 20 atm. Calculate (1) the work done by the gas, (2) the entropy change of the gas and (3) the entropy change of the environment.