An air traffic controller spots two airplanes at the same altitude converging to a point as they fly at right angles to each other. One airplane is 90 miles from the point and has a speed of 450 miles per hour. The other is 120 miles from the point and has a speed of 600 miles per hour.

a. At what rate is the distances between the planes decreasing?
b. How much time does the traffic controller have to get one of the planes on a different flight path?