The winds howl on a bitterly cold day at the quick change franchise. during the entire afternoon (a four hour period) only twenty-four cars are serviced. each car required four quarts of oil and a filter to complete. quick change pays $1.50 per quart of oil and charges $25 per customer. employees make $10 per hour whether they are changing oil or waiting for customers to arrive. the quick change operations manual has established 15 minutes as an appropriate duration for an oil change. what is an appropriate measure of efficiency?