Find flight occupancy by fare

For each departure airport, calculate the average occupancy rate of business and economy class flights in August 2017 (according to the actual departure date). Average occupancy is calculated as the percentage of occupied seats out of the total number of seats in a given class.
Display the result in three columns:
departure_airport — departure airport code
average_business_occupancy — average occupancy rate of business class seats (as a percentage, rounded to two digits)
average_economy_occupancy — average occupancy rate of economy class seats (as a percentage, rounded to two digits)