Check the picture below.
since chords NQ and MP cross the center of the circle at R, that means that those two chords are diametrical chords and the angles made by both are vertical angles and thus twin angles, namely both are 18° as you see in the picture, so the angle NMP in magenta is really 162° + 18° + 18° = 198°, and we know the radius NR is 8.
[tex]\textit{arc's length}\\\\ s=\cfrac{r\pi \theta }{180}~~ \begin{cases} r=radius\\ \theta =\stackrel{degrees}{angle}\\[-0.5em] \hrulefill\\ r=8\\ \theta =198 \end{cases}\implies s=\cfrac{(8)\pi (198)}{180}\implies s\approx 27.6[/tex]
