ANSWER
[tex]\begin{gathered} 20^2=13^2+b^2 \\ b\approx15.2ft \end{gathered}[/tex]
EXPLANATION
To find the length of the missing side, we have to apply the Pythagoras theorem:
[tex]hyp^2=a^2+b^2[/tex]
where
hyp = hypotenuse of the triangle
a and b are the length of the legs of the triangle
From the question:
[tex]\begin{gathered} \text{hyp}=20ft \\ a=13ft \end{gathered}[/tex]
Therefore, we have that:
[tex]20^2=13^2+b^2[/tex]
That is the equation that can be used to find the length of the missing side.
To find b, collect like terms and simplify:
[tex]\begin{gathered} 400=169+b^2 \\ b^2=400-169 \\ b^2=231 \\ \Rightarrow b=\sqrt[]{231} \\ b\approx15.2ft \end{gathered}[/tex]
That is the length of the missing side to the nearest tenth.
