Explanation:
We have to get one positive 7y so,
4x-7y=5
9x-7y=-15
multiply anyone of the equation by -1. I choose the first one so,
4x+7y=-5
9x-7y=-15
we can now cancel the y's so the equation will be left with
-4x=-5
9x=-15
add the equations
5x=-20
divide by 5 n u get
x=-4
now plug in the x value in any one of the
equations
I choose the first one so,
4(-4)-7y=5
-16-7y=5
add 16 to both sides
-7y=21
divide by -7
y=-3.
finally check.