$\left\{\begin{matrix}x=\frac{3Ya}{28IS}\text{, }y=\frac{a}{28}\text{, }&I\neq 0\text{ and }S\neq 0\\x\in \mathrm{C}\text{, }y=\frac{a}{28}\text{, }&\left(a=0\text{ and }I=0\right)\text{ or }\left(Y=0\text{ and }I=0\right)\text{ or }\left(Y=0\text{ and }S=0\text{ and }I\neq 0\right)\text{ or }\left(a=0\text{ and }S=0\text{ and }I\neq 0\right)\end{matrix}\right.$

$\left\{\begin{matrix}x=\frac{3Ya}{28IS}\text{, }y=\frac{a}{28}\text{, }&I\neq 0\text{ and }S\neq 0\\x\in \mathrm{R}\text{, }y=\frac{a}{28}\text{, }&\left(a=0\text{ and }I=0\right)\text{ or }\left(Y=0\text{ and }I=0\right)\text{ or }\left(Y=0\text{ and }S=0\text{ and }I\neq 0\right)\text{ or }\left(a=0\text{ and }S=0\text{ and }I\neq 0\right)\end{matrix}\right.$