[tex] \left \{ {{10x-7=y} \atop {3y+9=x}} \right. \\\\substitution\ method\\\\10(3y+9)-7=y\\\\
30y+90-7=y\\\\
30y+83=y\ \ \ \ | subtract\ 30y\\\\
83=-29y\ \ \ | divide\ by\ -29\\\\
y=-\frac{83}{29}\\\\
x=3y+9=3*(-\frac{83}{29})+9=\frac{178}{29}[/tex]
