



 
Hi Frank, I think the angle you need is the angle ABC which measures 67.5 degrees. Suppose the side length AB is s feet. I'm not sure which distance is 10 feet. If it is the distance from A to E then as Stephen showed s is 0.4142 times the distance from A to E so If the distance from A to D is 10 feet then since triangle AED is a right triangle we can use Pythagoras' theorem to find s. ED = 1/0.4142 s and ED = s so
and hence
Thus
and
I hope this helps,  


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