It is thought that people develop respiratory infections during air travel because much of the airplane cabin air is recirculated. Airlines claim that using only fresh air in the cabins is too costly since at an altitude of 30 000 feet the outside conditions are −50^◦C and 0.1 bar, so that the air would have to be compressed and heated before being introduced into the cabin. The airplane cabin has a volume of 100 m³ with air at the in-flight conditions of 25^◦C and 0.8 bar. What would be the cost of completely refreshing the air every minute if air has a heat capacity of C^∗_P = 30 J/(mol K) and energy costs $0.2 per kW hr?