$$2x+3y-4z-1; Q=2y+3x-4z+1$$
$x=\frac{3Q}{5}+\frac{4z}{5}-\frac{2a}{5}-1$
$y=\frac{3a}{5}+\frac{4z}{5}-\frac{2Q}{5}+1$
$z\in \mathrm{R}$
