Answer:
21 inches
Step-by-step explanation:
If [tex]\alpha[/tex] is the central angle, then the length of the arc on which this angle subtends is
[tex]l=r\cdot \alpha.[/tex]
Hence,
[tex]12\pi =\dfrac{4\pi}{7}\cdot r,\\ \\r=\dfrac{12\pi}{\frac{4\pi}{7}}=\dfrac{12\pi}{1}\cdot \dfrac{7}{4\pi}=21\ in.[/tex]
