Question 388226
Can't be done. 
To solve for three equations, you need three independent equations. 
With only two, you can get a variable in terms of the other variables. 
As in this case,
{{{4x+4y=2xy}}}
{{{4x-2xy=-4y}}}
{{{x(4-2y)=-4y}}}
{{{highlight(x=2y/(y-2))}}}
So now you have an equation for x and for z in terms of y. 
But that's the best you can do.