we have
6x+7y=4x+4y
we figure out that
the solution is ----> (x,-4)
substitute the value of y=-4 in the equation
6x+7*(-4)=4x+4*(-4)
6x-28=4x-16
Combine like terms
6x-4x=28-16
2x=12
x=12/2
x=6
So the the missing value is x=6.
