"An airplane is flying at a constant speed and altitude, on a line that will take it directly over a radar station located on the ground.

"An airplane is flying at a constant speed and altitude, on a line that will take it directly over a radar station located on the ground. At the instant when the airplane is 60,000 feet from the station, an observer in the station notes that its angle of elevation is 30 degrees and is increasing at the rate of 0.5 degrees per second. Find the speed of the airplane.