Solve the linear system LaTeX: \displaystyle \begin{cases} - 5 x - 6 y - 5 z = 3 \\ 7 x - 2 y - 2 z = 20 \\ 5 x - 3 y - z = 9 \\ \end{cases}

The Solution is LaTeX: \displaystyle (2, 2, -5) .