One mole of an ideal gas is taken round the cycle $A \to B \to C \to A$ shown in the pressure-temperature diagram. From A $(T_0, P_0)$ to B $(2T_0, 2P_0)$, the path is a straight line that passes through the origin when extended. From B to C the temperature stays at $2T_0$ while the pressure falls to $P_0$. From C back to A the pressure stays at $P_0$. The net work done by the gas in one cycle is

Fig. 1: Pressure-temperature diagram of the cycle: A (T0, P0) to B (2T0, 2P0) along a line through the origin, B to C at constant temperature 2T0 down to P0, and C back to A at constant pressure P0.