A plane flying with a constant speed of $9$ km/min passes over a ground radar station at an altitude of $11$ km and climbs at an angle of $25$ degrees. At what rate, in km/min is the distance from the plane to the radar station increasing $4$ minutes later?
Your answer: kilometers per minute.
Hint: The law of cosines for a triangle is $$c^2=a^2+b^2-2ab \cos(\theta)$$ where $\theta$ is the angle between the sides of length a and b.