A plane flying at an altitude of 4.0 mi is at a direct distance D = 1 16.0 + x" from an airport control tower, where x is the horizontal distance to the tower. If the plane's speed is 330 mi/h, how fast is D changing when x = 7.9 mi? D is changing at a rate of mi/h. Do not round until the final answer. Then round to the nearest ten as needed.)