4. For what values of $a$ is the system $\left\{\begin{array}{l}12 x^{2}+48 x-a+36=0 \\ (a+60) x-3(a-20)=0\end{array}\right.$ consistent? Solve the system for all permissible $a$.
Answer: 1) the system is consistent for $a=-12,0,180$;

2) when $a=-12$, $x=-2$; when $a=0$, $x=-1$; when $a=180$

$$
x=2 \text { . }
$$