\[\boxed{\text{998.\ }\text{еуроки}\text{-}\text{ответы}\text{\ }\text{на}\text{\ }\text{пятёрку}}\]
\[\textbf{а)}\ \left\{ \begin{matrix} x - 4 < 8\ \ \ \ \\ 2x + 5 < 13 \\ 3 - x > 1\ \ \ \ \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ }\left\{ \begin{matrix} x < 12 \\ 2x < 8 \\ - x > - 2 \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ \ }\]
\[\left\{ \begin{matrix} x < 12 \\ x < 4 \\ x < 2 \\ \end{matrix} \right.\ \Longrightarrow \ ( - \infty;2)\]
\[\textbf{б)}\ \left\{ \begin{matrix} 2x - 1 < x + 3 \\ 5x - 1 > 6 - 2x \\ x - 5 < 0\ \ \ \ \ \ \ \ \ \ \ \ \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ }\]
\[\ \left\{ \begin{matrix} x < 4 \\ 7x > 7 \\ x < 5 \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ \ }\left\{ \begin{matrix} x < 4 \\ x > 1 \\ x < 5 \\ \end{matrix} \right.\ \Longrightarrow \ \ (1;4)\]