An easy trig problem - angle of depression

Someone (a student perhaps?) sent me this problem


From a horizontal distance of 8.5km a pilot observes that the angle of depression of the top and base of a central tower are 30 degrees and 33 degrees respectively. 

Calculate 
a. the shortest distance between the pilot and the base of the central tower
b. the height of the central tower.


Actually, a good part of this problem is to draw the correct diagram. Once you have the image right, then the math should be fairly obvious.

But I'm going to help you out! Here's the image for this situation:
(not to scale)


The solution is posted here.

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