Air from a line at 12 MPa, 15?C flows into a 500-L rigid tank that initially contained air at ambient conditions, 100 kPa, 15?C. The process occurs rapidly and is essentially adiabatic. The valve is closed when the pressure inside reaches some value, P2. The tank eventually cools to room temperature, at which time the pressure inside is 5 MPa. What is the pressure P2? What is the net entropy change for the overall process?