Answer
The area of a triangle is approximately $16$ square yards.
Work Step by Step
The area of a triangle is calculated using Heron's formula where $s$ is equal to half the perimeter of the triangle. The area of the triangle is given by
$\begin{align}
& A=\sqrt{s\left( s-a \right)\left( s-b \right)\left( s-c \right)} \\
& \\
\end{align}$
where
$\begin{align}
& s=\frac{1}{2}\left( a+b+c \right) \\
& s=\frac{1}{2}\left( 13+9+5 \right)=13.5 \\
\end{align}$
By substituting the values of s and a, b, c we get,
$\begin{align}
& A=\sqrt{13.5\left( 13.5-13 \right)\left( 13.5-9 \right)\left( 13.5-5 \right)} \\
& A=\sqrt{258.1875}\simeq 16 \\
\end{align}$
