Paper folding project (resolved)

Hullo, I've just been given this math project, and I'm stuck.

Code:

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You have a sheet of paper 6 units wide and 25 units long,
oriented like so:
6
_____
|  |
|  | 25
|  |
|___|



fold the lower right hand corner over so that it touches the left side.
http://www.darkvariant.com/images/paper.GIF
Your task is to fold the paper in such a way so that the length
of the crease is minimized.  What is the length of the crease?
1. Solution must include calculus methods.
2. Answer must be justified.
3. Calculator may be used.

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When i first looked at this, I thought either related rates, or perhaps limits. I played around with it and tried to write an equation for the length of the crease via the 4 right triangles that are formed, but there were just too many darn variables :P
Any help would be appreciated. I don't want any answers or complete walkthroughs, just point me in the right direction if you can.

Resolved. I didn't notice that the fold was 6-x since it was just x translated over..anyhoo, thanks anways guys.