Use Pythagorean theorem:
[tex]hypotenuse^2=base^2+perpendicular^2[/tex]According to question
base = 13
perpendicular = 13
[tex]\begin{gathered} \text{hypotenuse}^2=\text{base}^2+\text{perpendicular}^2 \\ h^2=13^2+13^2 \\ h^2=169+169 \\ h^2=338 \\ h=\sqrt[]{338} \\ h=18.38 \end{gathered}[/tex]So the hypotenuse is 18.38 inches