Question 1049032
*[illustration Capture.JPG].
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No sure which measurements you have.
Here's the problem setup.
It leaves you with a triangle on top of a rectangle.
So the triangle is a 12-78-90 degree triangle.
Since you know one of the lengths of the triangle (not sure if you mean side or hypotenuse), then you can solve for the other sides. 
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Repost if you have a different diagram.