An angle such as $\frac{?}{{?}_{A}BC}$ is called an inscribed angle and it can be proved that the measure $($in degrees$)$ of an inscribed angle is half the measure $($in degrees$)$ of the arc it cuts. So if the measure of arcAC is $60,$ then the measure of $\frac{?}{{?}_{A}BC}$ would be $30.$ Recall that $\frac{?}{{?}_{A}DC}$ is a central angle.

If $\frac{m}{{?}_D}=24$ and the circumference of the circle is $210$ inches, then what is the length of arcAC $?$

The length of arcAC is $$ inch$($es$)$

$($Type an integer or a decimal.$)$