\[1 < a < 2\ \ \ и\ \ \ 0 < b < 4\]
\[+ \left| \begin{matrix} 3 < 3a < 6 \\ 0 < 4b < 16 \\ \end{matrix} \right.\ \]
\[\overline{\ \ \ \ 3 < 3a + 4b < 22}\]
\[Ответ:\ \ 3 < 3a + 4b < 22.\]