So basically here is the answer mate!
2x + 7y = 3-------------------------(substitute x's value here, i.e., x = -4y)
2( -4y ) + 7y = 3
-8y + 7y = 3
-1y = 3
y = -3------------------------( 1 )
Since x = -4y
= -4 ( -3 ) --------------------------( since we found the value of y)
= 12
Here is the answer for x = 12 , y = -3
Mark my anwer as the brainliest please ! :)