Question

How do you do this 10x-7=y 3y+9=x

Answer 1

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