notice, the diameter for the smaller circle is 19.2, thus its radius is half that, or 9.6.
the radius from the center to the outer circle is then 9.6 + 18.1.
[tex]\bf \textit{area of a circular ring}\\\\
A=\pi (R^2-r^2)~~
\begin{cases}
R=\textit{radius from center}\\
\qquad \textit{to outer circle}\\
r=\textit{radius from center}\\
\qquad \textit{to inner circle}\\
----------\\
r=\frac{19.2}{2}\\
\qquad 9.6\\\\
R=\frac{19.2}{2}+18.1\\
\qquad 9.6+18.1\\
\qquad 27.7
\end{cases}
\\\\\\
A=\pi (27.7^2-9.6^2)[/tex]
