Open Question: Optimization problem, please help?

To get the best view of the Statue of Liberty, you should be at the position where ? is a maximum. Suppose the statue stands 80 meters high, including the pedestal, which is 40 meters high.

Here is the picture:
http://www.webassign.net/hgmcalc/4-5-34.gif

How far from the base should you be? Give an exact answer.
[Hint: Find a formula for ? in terms of your distance, d, from the base. To do this, you can first write ? = ß - a. Then use trigonometry to express ß and a in terms of d.]

Please show steps so I can understand! Thanks!

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