\[\left\{ \begin{matrix} 4x - y = 15 \\ 8x + y = 9\ \ \\ \end{matrix} \right.\ ( + )\]
\[12x = 24\]
\[x = 2.\]
\[y = 4x - 15 = 8 - 15 = - 7.\]
\[Ответ:(2; - 7).\]