$$\left. \begin{array} { l } { x y } \\ { : \quad x + 4 y = 14 } \end{array} \right.$$
$x=14-4y\text{, }y=\frac{\sqrt{49-4z}+7}{4}\text{, }z\leq \frac{49}{4}$
$x=14-4y\text{, }y=\frac{-\sqrt{49-4z}+7}{4}\text{, }z\leq \frac{49}{4}$
