[ $[\quad$ Similar figures $\quad]$

Several circles are inscribed in an angle, their radii increasing. Each subsequent circle touches the previous one. Find the sum of the lengths of the second and fourth circles, if the length of the third is $18 \pi$, and the area of the circle bounded by the first circle is $\pi$.

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Figures consisting of two adjacent circles are similar to each other.

## Answer

$60 \pi$.