A piston-cylinder device contains 5 kg of air at 400 kPa and 30C. During a quasi-equilibium isothermal

Question:

A piston-cylinder device contains 5 kg of air at 400 kPa and 30°C. During a quasi-equilibium isothermal expansion process, 15 kJ of boundary work is done by the system, and 3 kJ of paddle-wheel work is done on the system. The heat transfer during this process is
(a) 12 kJ
(b) 18 kJ
(c) 2.4 kJ
(d) 3.5 kJ
(e) 60 kJ