Chọn D
Ta có \(f'\left(x\right)=3x^{2} +6x=3x\left(x+2\right)\)
\(f'\left(x\right)=0\Leftrightarrow \left[\begin{array}{l} {x=0\, \, \left(t/m\right)} \\ {x=-2\, \, \left(l\right)} \end{array}\right. \)
Ta có: \(f\left(0\right)=-4;f\left(-1\right)=-2;f\left(2\right)=16\)
Suy ra: \(M={\mathop{Max}\limits_{\left[-1;2\right]}} f\left(x\right)=f\left(2\right)=16;m={\mathop{Min}\limits_{\left[-1;2\right]}} f\left(x\right)=f\left(0\right)=-4
\Rightarrow M+3m=4.\)