3. In the figure shown above, a hot air balloon rising straight up from the ground is tracked by a television camera 300 ft from the liftoff point. At the moment the camera's elevation angle is a/6, the balloon is
rising at the rate of 80 ft/min . At what rate is the angle of elevation changing at that moment?
(A) 0.12 radian per minute
(B) 0.16 radian per minute
(C) 0.2 radian per minute
(D) 0.4 radian per minute
(E) 0.6 radian per minute