An airplane flys at a constant altitude of 2 miles and a constant speed of 600 miles per hour on a straight course that will take it directly over a kangaroo on the ground. How fast is the angle of elevation of the kangaroo's line of sight increasing when the distance from the kangaroo to the plane is 3 miles? Give your answer in radians per minute.

Answer: .
Hint: The angle of elevation is that angle that the line of sight makes with the horizontal. Construct a triangle representing the situation. Use this to get a equation first involving $x$ and $y$, then differentiate to involve $\displaystyle\frac{\hbox{d}x}{\hbox{d}t}$ and $\displaystyle\frac{\hbox{d}y}{\hbox{d}t}$. Think about what it means that the plane is getting closer to the kangaroo.