The cost for operating a commercial truck is kn, where k is a constant of proportionally, v is velocity in miles per hours and n is the trip length in miles. It is estimated that at 85 mph, the average cost of operation is $52 per mile. The truck owner wants to minimize the cost of operation, which requires balancing against the cost of delays and unscheduled maintenance, which is assumed to be $10 per hour. What is the optimum velocity required to minimize the total costs?