check the picture below.
so... notice, the larger green circle, has a radius of 22.
now, the blue smaller circle, is taking up half of the diameter of the green one, so, the diameter for the small one is 22, and its radius is half that, or 11.
[tex]\bf \textit{circumference of a circle}\\\\
C=2\pi r\\\\
-------------------------------\\\\
\stackrel{\textit{large green circle}}{C=2\cdot \pi \cdot 22}\implies C=44\pi \qquad\qquad \qquad \stackrel{\textit{small blue circle}}{C=2\cdot \pi \cdot 11}\implies C=22\pi [/tex]
