[tex]\begin{cases}5x+4y=-30\ \ / \cdot (-3) \\3x-9y=-18\ \ / \cdot 5 \end{cases}\\\\ \begin{cases}-15x-12y=90 \\15x-45y=-90 \end{cases}\\+\ --------\\ -57y=0 \\ y=0 \\\\ 5x+4y=-30\\5x+4 \cdot 0=-30 \\5x=-30 \ \ / :5 \\x=-\frac{30}{5}\\x=-6 \\ \\Answer : \\\\ \begin{cases} x=-6 \\ y=0 \end{cases} [/tex]
