\[R = 24\ см;\ \ \ L = 3\pi\ см:\]
\[L = \frac{\pi\text{Ra}}{180{^\circ}}\text{\ \ }\]
\[a = \frac{180{^\circ}L}{\pi R}\]
\[a = \frac{180{^\circ} \bullet 3\pi}{\pi \bullet 24} = 22,5{^\circ}.\]
\[Ответ:\ \ 22,5{^\circ}.\]