$\left\{\begin{matrix}a\in \left(\frac{7\left(X-7\right)}{4},\infty\right)\cup \left(-\infty,0\right)\text{, }&X>7\\a\neq 0\text{, }&X=7\\a\in \left(0,\infty\right)\cup \left(-\infty,\frac{7\left(X-7\right)}{4}\right)\text{, }&X<7\end{matrix}\right.$

$\left\{\begin{matrix}X>\frac{4a}{7}+7\text{, }&a<0\\X<\frac{4a}{7}+7\text{, }&a>0\end{matrix}\right.$