Question: Don't Understand This Deriative Problem

 

For the last hour I have been starring at this problem.  Each time that I think I understand what is being asked my mind confuses itself.

Here is the problem.

http://img262.imageshack.us/img262/8387/helpxz2.png

 

My understanding is that I need to take the partial deriative of this function to get the given result.  However, what I need to do (let me know if I am incorrect) is figure out how to take the partial derative to get the input.

Am I right, or have I confused myself again?

Thanks for any input.

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