The correct option will be the last one: (-5, 8)
Explanation
[tex] 7x + 2y = -19...................(1) \\\\-x + 2y = 21.........................(2) [/tex]
According to substitution method, first we will isolate either [tex] x [/tex] or [tex] y [/tex] from any of the equation. So, we are solving the equation (2) for [tex] x [/tex] now...
[tex] -x+2y=21\\ \\ -x= -2y+21\\ \\ x= 2y-21 [/tex]
Now we will plug this [tex] x= 2y-21 [/tex] into equation (1) in place of [tex] x [/tex]...
[tex] 7(2y-21)+2y= -19\\ \\ 14y-147+2y=-19\\ \\ 16y-147=-19\\ \\ 16y=-19+147\\ \\ 16y=128\\ \\ y= \frac{128}{16}=8 [/tex]
By plugging [tex] y=8 [/tex] into the equation [tex] x= 2y-21 [/tex] , we will get...
[tex] x=2(8)-21= 16-21=-5 [/tex]
So, the solution of the system is (-5, 8)
