A 40 L heat exchanger that contains water, initially at the same temperature as the environment, 5 C, is turned on and is rated for 3 kW. The exchanger is used to heat the air in a 50 m room that is initially at 5 C until it reaches the desired 22 C. The room loses heat to its surroundings at a rate of 1.2 kW. When the heating is complete the temperature of the water is 17 C. Given p = 1000 kg/m3 and c=4.18 kJ/kg.K for water, determine (a) how long the exchanger is on for, (b) the exergy destruction, and (c) the second-law efficiency for this exchange