Check the picture below.
we know the diameter MK is 9 units, so the radius must be half that, or 4.5.
[tex]\textit{arc's length}\\\\ s=\cfrac{\theta \pi r}{180}~~ \begin{cases} r=radius\\ \theta =\stackrel{degrees}{angle}\\[-0.5em] \hrulefill\\ r=4.5\\ \theta =218 \end{cases}\implies \begin{array}{llll} s=\cfrac{(218)\pi (4.5)}{180}\implies s=5.45\pi \\\\\\ s\approx 17.1 \end{array}[/tex]
