[tex]\bf s=\cfrac{\pi \theta r}{180}\implies \cfrac{180s}{r\pi }=\theta\quad
\begin{cases}
r=radius\\
s=\textit{lenght of arc}\\
\theta=\textit{central angle}\\
\quad\ in\ degrees\\
--------\\
r=6\\\\
s=\frac{7\pi }{3}
\end{cases}\implies \cfrac{180\cdot \frac{7\pi }{3}}{6\pi }=\theta[/tex]