Question

What is the solution of the system? Use either the substitution method or the elimination method. 7x + 2y = −197x + 2y = −19 −x + 2y = 21

Answer 1

The answer is (−5, 8) i did the quiz and got it right!
hope this helps

Answer 2

The correct option will be the last one: (-5, 8)

Explanation

$7x + 2y = -19...................(1) \\\\-x + 2y = 21.........................(2)$

According to substitution method, first we will isolate either $x$ or $y$ from any of the equation. So, we are solving the equation (2) for $x$ now...

$-x+2y=21\\ \\ -x= -2y+21\\ \\ x= 2y-21$

Now we will plug this $x= 2y-21$ into equation (1) in place of $x$...

$7(2y-21)+2y= -19\\ \\ 14y-147+2y=-19\\ \\ 16y-147=-19\\ \\ 16y=-19+147\\ \\ 16y=128\\ \\ y= \frac{128}{16}=8$

By plugging $y=8$ into the equation $x= 2y-21$ , we will get...

$x=2(8)-21= 16-21=-5$

So, the solution of the system is (-5, 8)