\[- 3 < a < - 2\ \ \ \ и\ \ \ 1 < b < 2\]
\[3 > - a > 2;\ \ \ \ \ \ \ \ 3 < 3b < 6\]
\[+ \left| \begin{matrix} 2 < - a < 3 \\ 3 < 3b < 6 \\ \end{matrix} \right.\ \]
\[\overline{\ \ \ \ 5 < - a + 3b < 9}\]
\[Ответ:5 < - a + 3b < 9.\]