Air is contained in a variable-load cylinder-piston device equipped with a paddle wheel. Initially, the air is at 500 kPa and 27 degree C. The paddle wheel is now turned by an external electric motor until 50 kJ/kg of work has been transfered to the ar. During the process, heat is transferred to maintain the constant air temperature while allowing the gas volume to triple. Calculate the amount of heat transfer during the process (kJ/kg).