Hey there! :)
We are given two equations.
Equation 1 is : x + y = -3
Equation 2 is : 5x + 7y = -9
In order to solve this, we have to multiply ALL of equation #1 by 5, so that both equations have "5x" in it.
Equation 1: 5(x + y = -3)
Simplify.
5x + 5y = -15
This new equation is now being called equation #3.
So, line up equations #2 and #3.
Equation 2 : 5x + 7y = -9
Equation 3 : 5x + 5y = -15
Notice how the x's, y's, and regular numbers are lined up with one another. Using that, we can subtract equation #3 from #2.
5x - 5x = 0
7y - 5y = 2y
-9 -(-15) = 6
So, we now have this :
2y = 6
Divide both sides by 2.
2y ÷ 2 = 6 ÷ 2
Simplify.
y = 3
So, now that we have the value of y, very simply plug in 3 for y in equation #1.
Equation 1 : x + y = -3
x + (3) = -3
Subtract 3 from both sides.
x + 3 - 3 = -3 - 3
Simplify.
x = -6
So, our answers are :
x = -6, y = 3
~Hope I helped!~