\[36,\ \ \ 20,\ \ \ 11\frac{1}{9},\ldots\]
\[q = \frac{20}{36} = \frac{5}{9};\]
\[S = \frac{b_{1}}{1 - q} = \frac{36}{1 - \frac{5}{9}} = \frac{36}{\frac{4}{9}} =\]
\[Ответ:81.\]