\[\left\{ \begin{matrix} 6x - y = 15 \\ 5x + 3y = 1 \\ \end{matrix} \right.\ \Longrightarrow \left\{ \begin{matrix} y = 6x - 15\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \\ 5x + 3 \cdot (6x - 15) = 1 \\ \end{matrix} \right.\ \]
\[5x + 18x - 45 = 1\]
\[23x = 46\]
\[x = 2.\]
\[y = 6 \cdot 2 - 15 = 12 - 15 = - 3.\]
\[\left\{ \begin{matrix} x_{0} = 2\ \ \ \\ y_{0} = - 3 \\ \end{matrix} \right.\ \]
\[x_{0} + y_{0} = 2 - 3 = - 1.\]
\[Ответ:2) - 1.\]