In a laboratory experiment, 0.300 moles of helium is used as the working fluid in a thermal engine. The helium undergoes an isothermal expansion from an initial volume of 2.50 × 10^-3 m³ to 7.50 × 10^-3m³ at a temperature of 400 K, followed by an isochoric cooling to 320 K, an isothermal compression to a volume of 2.50 × 10^-3 m³, and finally, isochoric heating to a temperature of 400 K. Calculate i) the work done in one cycle and ii) the thermal efficiency of the engine.