Bristol Car Service offers airport service in a mid-size city. Bristol charges $50 per trip to or from the airport. The variable cost for a trip totals $12, for fuel, driver, and so on. The monthly fixed cost for Bristol Rainbow Tours is $2, 736. a. How many trips must Bristol sell every month to break even? b. Bristol's owner believes that 90 trips is a reasonable forecast of the average monthly demand. What is the margin of safety in terms of the number of airport trips