Air within a piston-cylinder assembly executes a Carnot heat pump cycle, as shown in the figure below. For the cycle, $T_H = 600 K$ and $T_C = 300 K$. The energy rejected by heat transfer at 600 K has a magnitude of 625 kJ per kg of air. The pressure at the start of the isothermal expansion is 325 kPa.
Assuming the ideal gas model for the air, determine:
(a) the magnitude of the net work input, in kJ per kg of air, and
(b) the pressure at the end of the isothermal expansion, in kPa.