The arc length formula is :
[tex]l=r\theta[/tex]
where r = radius
θ = angle in radians
and l = arc length
From the problem, the arc length is 18π/7 and the angle is 6π/7.
Using the formula above :
[tex]\begin{gathered} \frac{18\pi}{7}=r(\frac{6\pi}{7}) \\ 18\pi=r(6\pi) \\ r=\frac{18\pi}{6\pi} \\ r=3 \end{gathered}[/tex]
ANSWER :
The radius is 3
