Cha658pter 9 - 9.3 - Multivariable Linear Systems - 9.3 Exercises - Page 658: 20

$x=-7; y=-14$

Multiply the second equation by $-1$, then add it to equation $1$. $2x-y-x+y=0-7 \\ \implies x=-7$ Now, we will plug the value of $x$ into the first equation to find the value of $y$. We get: $2(-7)-y=0 \\ \implies y=-14$ Thus, $x=-7; y=-14$