\[\boxed{\text{290}\text{\ (290)}\text{.}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\text{M\ }(3;\ - 6):\]
\[y = ax^{2}\]
\[- 6 = a \cdot 9\]
\[a = - \frac{6}{9}\]
\[a = - \frac{2}{3}.\]
\[Ответ:\ a = - \frac{2}{3}\text{.\ }\]