Chapter 3 - Section 3.1 - Systems of Linear Equations in Two Variables - 3.1 Exercises - Page 226: 28

$x=-1$ $y=3$

First, we have to solve the second equation for $y$ and after that, we can substitute this expression in the first equation: $4+7x=-y$ $-4-7x=y$ $6x-y=-9$ $6x-(-4-7x)=13x+4=-9$ $13x=-13$ $x=-1$ $-4-7x=-4-7(-1)=3=y$ We need to check, if it is the right solution, we substitute x with $-1$ and y with $3$: $6(-1)-3=-9$ $\checkmark$ $4+7(-1)=-3$ $\checkmark$