Thermodynamically efficient or not?

A linear diatomic ideal gas (with adiabatic exponent, $\gamma = 1.4$ ) was initially at $T = 260^{\circ} C$ , $P = 700 \ \text{Pa}$ and occupied a volume, $V = 28 \ \text{L}$ . The gas is now taken through three thermodynamic processes as follows:

• First: Gas is expanded isobarically to a volume of $84 \ \text{L}$ (Process AB) .

• Second: It is taken through a polytropic process having equation $PV^n = \text{constant}$ with $n = 1.5$ (Process BC) .

• Third: After the polytropic process is carried out, the gas comes back to its initial temperature and an isothermal process is carried out in the third step and the gas returns back to its initial state (Process CA) .

Find the percentage efficiency $\eta$ of the above cycle.