$$\left. \begin{array} { l } { + f x + c = 9 x } } \end{array} \right.$$
$\left\{\begin{matrix}x=-\frac{c}{f-9}\text{, }&f\neq 9\\x\in \mathrm{C}\text{, }&c=0\text{ and }f=9\end{matrix}\right.$
$\left\{\begin{matrix}x=-\frac{c}{f-9}\text{, }&f\neq 9\\x\in \mathrm{R}\text{, }&c=0\text{ and }f=9\end{matrix}\right.$
