According to the information the triangle is formed by the sides of the 3 squares, if you mind the missing side of the triangle formed by the 5inch and 13inch sides you find the side of the third square.
Use the pythagorean
[tex]\begin{gathered} h^2=x^2+y^2 \\ 13^2=5^2+y^2 \\ 13^2-5^2=y^2 \\ 169-25=y^2 \\ 144=y2 \\ \sqrt[]{144}=y \\ 12=y \end{gathered}[/tex]
The lenght of a side in the third square could be 12 inches.
