The arc length formula is :
[tex]\text{arc}=r\theta[/tex]
where r = radius and the angle is in radians
From the problem, the arc length is 21π units and the radius is 15 units.
Using the formula above :
[tex]\begin{gathered} 21\pi=15\theta \\ \theta=\frac{21\pi}{15} \\ \theta=\frac{7}{5}\pi \end{gathered}[/tex]
ANSWER :
A.
