I need to help finding the length of the arc shown in red..

We have the next formula to find the length is
[tex]\text{arc length }=\text{ 2}\pi r(\frac{\theta}{360})[/tex]where
r=10
theta=45°
[tex]\begin{gathered} \text{arc length=}2\pi(10)\frac{45}{360}=\frac{5}{2}\pi \\ \end{gathered}[/tex]the arc length is 5/2 pi cm