Power-cycle claims between reservoirs at 1500 K and 450 K — decide whether each is reversible, irreversible or impossible: a) Q_{H} = 600 kJ, W = 300 kJ, Q_{C} = 300 kJ; b) Q_{H} = 400 kJ, W = 280 kJ, Q_{C} = 120 kJ; c) Q_{H} = 700 kJ, W = 300 kJ, Q_{C} = 500 kJ; d) Q_{H} = 800 kJ, W = 600 kJ, Q_{C} = 200 kJ.