[tex]\textit{arc's length}\\\\s=\cfrac{\theta \pi r}{180}~~\begin{cases}r=radius\\\theta =\stackrel{degrees}{angle}\\[-0.5em]\hrulefill\\r=13.5\\\theta =120\end{cases}\implies \begin{array}{llll}s=\cfrac{(120)\pi (13.5)}{180}\implies s=9\pi \\\\\\s\approx 28.27\end{array}[/tex]
