Two stationary patrol cars equipped with radar are 5 miles apart on Highway 41. As Alex's car passes the first patrol car, its speed is clocked at 55 mph. Four minutes later, when Alex passes the second patrol car, his speed is clocked at 50 miles per hour. Prove that Alex must have exceeded the 55 mph speed limit at some time during that four minutes and deserves his speeding ticket. Use Calculus.