A truck driving over a flat interstate at a constant rate of 50 mph gets 4 miles to the gallon. The fuel costs $3.95 per gallon. For each mile per hour increase in speed, the truck loses a tenth of a mile per gallon in mileage. Drivers get paid $55 per hour in wages and fixed costs for running the truck amount to $20 per hour. What constant speed, between 50 and 65 mph, should the dispatcher require on a straight run of 260 miles of Kansas Interstate to minimize the total cost of operating the truck?