I believe your mistake is that you are trying to use the sector area formula ti find arc length when there is already a formula for it. The formula for it is [tex]2r\pi( \frac{degree}{360} )[/tex] So first substitute the values in and then simplify! [tex]2(10.5)\pi( \frac{118}{360} )[/tex] Now simplify! 21 × 118 is 2478 so it's [tex] \frac{2478}{360} \pi[/tex] When divided ou and multiplied, this is 21.62cm!