Exergy destruction with heat transfer through wall

Heat transfer by conduction occurs through a wall of a house. The indoor air temperature is 20°C, the inside wall surface is 18°C, the outside wall surface is 7°C, and the outdoor air temperature is 0°C. The rate of heat transfer is 1200 W. Determine the: (a) exergy destruction in the wall (b) exergy destruction in an enlarged control volume Let T0= 0°C.