Precalculus (6th Edition) Blitzer

The required value is $x=-6,y=-2$
We have to multiply the second equation with 7 and add it to the first equation: \begin{align} & 2x-7y+7\left( 3x+y \right)=2+7\left( -20 \right) \\ & 2x-7y+21x+7y=2-140 \\ & 23x=-138 \\ & x=-6 \end{align} Substitute the value of $x=-6$ in the first equation: \begin{align} & 2\left( -6 \right)-7y=2 \\ & -12-7y=2 \\ & -7y=14 \\ & y=-2 \end{align}