Air expands irreversibly in a cylinder from P1 = 280 kPa, T1 = 60C, to P2 = 140 kPa. The air does work in the amount of 30 kJ/kg and 14 kJ/kg of heat is removed from the air during the expansion. The initial volume is 0.00878 m3. Calculate the entropy change of the air per kilogram.