\left\{ \begin{array}{l}5x + 6y = 17 \\ 9x - y = 7 \\ \end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}5x + 6(9x - 7) = 17 \\ y = 9x - 7 \\ \end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}59x = 59 \\ y = 9x - 7 \\ \end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}x = 1 \\ y = 2 \\ \end{array} \right.