\textbf{122-} The figure below shows the graph of the function with equation $f(x) = -x^4 + 4x^3 + ax^2 + b$. What is $a$?
\textit{[Figure: Graph of a polynomial function with a local maximum and minimum]}
\begin{itemize}
\item[(1)] $-18$
\item[(2)] $-15$
\item[(3)] $-12$
\item[(4)] $-9$
\end{itemize}