(c) $W_{AB} = - P_{0}V_{0},\ W_{BC} = 0$ and $W_{CD} = 4P_{0}V_{0}$ $\Rightarrow W_{ABCD} = - P_{0}V_{0} + 0 + 4P_{0}V_{0} = 3P_{0}V_{0}$
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.