Не знаю как решить, помогите

Решите задачу:

$f(x)=(x-6)(x+1)(x+2),\\ f(x)=0, (x-6)(x+1)(x+2)=0, \\ \left[\begin{array}{c}x-6=0,\\x+1=0,\\x+2=0;\end{array}\right. \left[\begin{array}{c}x=6,\\x=-1,\\x=-2;\end{array}\right. \\ x\ \textless \ -2, f(x)\ \textless \ 0,\\ -2\ \textless \ x\ \textless \ -1, f(x)\ \textgreater \ 0, \\ -1\ \textless \ x\ \textless \ 6, f(x)\ \textless \ 0, \\ x\ \textgreater \ 6, f(x)\ \textgreater \ 0; \\ x_{max}\in(-2;-1), x_{min}\in(-1;6); \\ x\in(-\infty;x_{max}), x\in(x_{min};+\infty) \ \ y\nearrow, \\ x\in(x_{max};x_{min}) \ \ y\searrow; \\ a=2, b=1, c=1, d=1; \\ a+2b+3c+4d=2+2+3+4=11.$