\[\boxed{\text{253\ (253).\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[y = \frac{k}{x};\ \ \ P( - 9,\ 18):\]
\[18 = \frac{k}{- 9}\]
\[k = - 9 \cdot 18\]
\[k = - 162.\]
\[Ответ:k = - 162.\]