Answer
See the graph below.
Work Step by Step
We know that:
$\bullet$ Isochoric process means the pressure is constant. In this process, the pressure doubled.
$\bullet$ Isobaric process means the volume is constant. In this process, the volume doubled.
$\bullet$ Isothermal process means the temperature is constant. In this process, the volume doubled again which means that the pressure is halved. Hence, $P_f=P$.
See the figure below.
