Answer
$9.42 \ cm$
Work Step by Step
Let $C$ be the circumference of a circle:
$C=2 \pi r$ or, $C=\pi d$
Plug in the given data to obtain:
$C=2\pi r=(2 \pi)(6) =12 \pi \ cm$
In order to get the arc length $l$, we need to multiply the circumference $C$ by $\dfrac{90^{\circ}}{360^{\circ}}$.
So, we have:
$l=\dfrac{90^{\circ}}{360^{\circ}} \times 12\pi=9.42 \ cm$
