[tex] \bf \textit{arc's length}\\\\s=\cfrac{\theta \pi r}{180}~~\begin{cases}r=radius\\\theta =angle~in\\\qquad degrees\\------\\r=3\\\theta =78\end{cases}\implies s=\cfrac{(78)\pi (3)}{180}\implies s=\cfrac{13\pi }{10} [/tex]
and you can round that up as needed.
