#### Answer

$r=8$ units

#### Work Step by Step

The radius of the circle can be found using the formula for the length of arc (s), which is $s=r\theta$.
Substitute the given values of $\theta$ and $s$ to obtain:
$s=r\theta
\\6\pi=r(\frac{3\pi}{4})
\\\frac{4}{3\pi} \cdot 6\pi=r(\frac{3\pi}{4})\cdot (\frac{4}{3\pi})$
$\\8=r$ units