A three-step cycle is undergone by 3.4 mol of an ideal diatomic gas:
(1) the temperature of the gas is increased from 210 K to 400 K at constanr volume;
(2) the gas is then isothermally expanded to its original pressure;
(3) the gas is then contracted at constant pressure back to its original volume. Throughout the cycle, the molecules rotates but do not oscillate. What is the efficiency of the cycle?