Answer
The arc should be $8.4in$ long.
Work Step by Step
$\theta = 80^\circ=\frac{80}{180}\pi=\frac{4}{9}\pi$
$D=12in$
$r=\frac{D}{2}=6in$
$s=r\theta = \frac{4}{9}\pi*6in\approx 8.4in$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.