\[\boxed{\text{999.\ }\text{еуроки}\text{-}\text{ответы}\text{\ }\text{на}\text{\ }\text{пятёрку}}\]
\[\textbf{а)}\ \left\{ \begin{matrix} 3 - 2a < 13 \\ a - 1 > 0\ \ \ \ \\ 5a - 35 < 0 \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ }\left\{ \begin{matrix} - 2a < 10 \\ a > 1\ \ \ \ \ \ \\ 5a < 35\ \ \ \\ \end{matrix} \right.\ \text{\ \ \ \ }\]
\[\ \left\{ \begin{matrix} a > - 5 \\ a > 1\ \ \ \\ a < 7\ \ \ \ \\ \end{matrix} \right.\ \Longrightarrow \ \ (1;7)\]
\[\textbf{б)}\ \left\{ \begin{matrix} 6 - 4a < 2 \\ 6 - a > 2\ \ \\ 3a - 1 < 8 \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ \ }\left\{ \begin{matrix} - 4a < - 4 \\ - a > - 4\ \ \\ 3a < 9\ \ \ \ \ \ \\ \end{matrix} \right.\ \text{\ \ \ \ }\]
\[\ \left\{ \begin{matrix} a > 1 \\ a < 4 \\ a < 3 \\ \end{matrix} \right.\ \Longrightarrow \ \ (1;3)\]
\[\textbf{в)}\ \left\{ \begin{matrix} 5a - 8 > 7 \\ 4 - a < 3\ \ \ \\ 2 - 3a > 10 \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ }\left\{ \begin{matrix} 5a > 15 \\ - a < - 1 \\ - 3a > 8 \\ \end{matrix} \right.\ \text{\ \ \ \ \ }\]
\[\ \left\{ \begin{matrix} a > 3\ \ \ \ \\ a > 1\ \ \ \ \\ a < - \frac{8}{3} \\ \end{matrix} \right.\ \Longrightarrow \ \varnothing\]