so hmm check the picture below
[tex]\bf s=\cfrac{r\pi \theta}{180}\qquad
\begin{cases}
s=\textit{length of the arc}\\
\theta=\textit{central angle in degrees}\\
r=radius\\
----------\\
r=36\\
\theta=140
\end{cases}\implies s=\cfrac{36\cdot \pi \cdot 140}{180}[/tex]
