Two commercial airplanes are flying at an altitude of 40,000 ft along straight-line courses that intersect at right angles. Plane A is approaching the intersection point at a speed of 422 knots (nautical miles per hour; a nautical mile is 2000 yd or 6000 ft). Plane B is approaching the intersection at 450 knots. At what rate is the distance between the planes changing when Plane A is 4 nautical miles from the intersection point and Plane B is 6 nautical miles from the intersection point?

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