One Mole of a Monatomic Ideal Gas at a Pressure

One mole of a monatomic ideal gas at a pressure of 3.0 atm and a volume of 30 L is isothermally expanded to a pressure of 1.0 atm and a volume of 90 L.Afterwards it is compressed at a constant pressure until its volume is 30 L and then it's pressure is increased at a constant volume back to the original volume of 30 L as shown in the PV diagram.What is the efficiency of this heat engine cycle?

A) 0.21
B) 0.43
C) 0.57
D) 0.67
E) 0.91