A delivery driver typically completes a 100-mile route at an average speed of 50 miles per hour to meet a deadline. Today, due to an unexpected road closure, he had to travel the first 40 miles at an average speed of 40 miles per hour. To ensure he still meets his deadline, at what average speed, in miles per hour, must he travel the remaining 60 miles of the route?
55
58
60
62
65
