Estimating a cost function, high-low method. FlyHigh Vacations offers helicopter service fromsuburban towns to Heathrow Airport in the United Kingdom. Each of its 10 helicopters makes between 1,000and 2,000 round-trips per year. The records indicate that a helicopter that has made 1,000 round-trips in theyear incurs an average operating cost of $350 per round-trip, and one that has made 2,000 round-trips in theyear incurs an average operating cost of $300 per round-trip