A heat engine constructed with one mole of an ideal monatomic gas operates on a reversible cycle a→b→c→d→a. The system goes from a→b in a isochoric process from Pa (pressure ) to Pb=4Pa. The system...

A heat engine constructed with one mole of an ideal monatomic gas operates on a reversible cycle a→b→c→d→a. The system goes from a→b in a isochoric process from Pa (pressure ) to Pb=4Pa. The system then expands in an isothermal process b→cf from Va to 2Va. A second isochoric process c→d takes the system to pressure back to Pa after which an isobaric process d→a return the system to its original state.

what is the energy efficiency?