$a)$

$\{\begin{array}{l}w\left(-1\right)=4\\ w\left(2\right)=20\end{array}$

$\{\begin{array}{l}-3\cdot {\left(-1\right)}^3+a\cdot {\left(-1\right)}^2+b\cdot \left(-1\right)+2=4\\ -3\cdot 2^3+a\cdot 2^2+b\cdot 2+2=20\end{array}$