[tex]\bf \textit{circumference of a circle}\\\\ C=2\pi r~~ \begin{cases} r=radius\\[-0.5em] \hrulefill\\ r=11 \end{cases}\implies C=2\pi (11)\implies C=22\pi \\\\\\ \stackrel{~\hfill \textit{a semicircle has half of that}}{C=\cfrac{22\pi }{2}\implies C=11\pi \implies C\approx 34.56}[/tex]
