An engine using 1 mol of an ideal gas ini- tially at 22.3 L and 337 K performs a cycle consisting of four steps: 1) an isothermal expansion at 337 K from 22.3 L to 39 L ; 2) cooling at constant volume to 227 K; 3) an isothermal compression to its original volume of 22.3 L; and 4) heating at constant volume to its original temperature of 337 K . Find its efficiency. Assume that the heat capacity is 21 J/K and the univer- sal gas constant is 0.08206 L - atm/mol/K = 8.314 J/mol/K