Draw V-T curve

V-T curve for all process is shown in figure. The initial state is represented by the point. In the first step, it is isothermally expanded to a volume 4V. This is shown by AB. Then the pressure is kept constant and the gas is compressed to the initial volume V. From the identity gas equation, V/T is constant at constant pressure (PV =nRT). Hence, the process shown by a line BC which passes through the origin. At point C, the volume is V. In the first step, the gas is heated at constant volume to a temperature T. This is shown by CA. The final state is the same as the initial state.