Answer
$0.444 \text{ radians}$
Work Step by Step
$\because A = \dfrac{1}{2}r^2 \theta$
where
$r$: Radius of the circle
$\theta$: Central angle that subtends the arc (in radians)
$A$: Area of the sector of the circle formed by the central angle $\theta$
Derive the formula for $\theta$:
\begin{align*}
A&=\frac{1}{2}r^2\theta\\\\
2A&=r^2\theta\\\\
\dfrac{2A}{r^2}&=\theta\\\\
\end{align*}
Using this formula gives:
$\theta = \dfrac{2 A}{r^2}$
$\theta = \dfrac{2\times 8}{6^2} = \boxed{0.444 \text{ radians}}$
