\left[
\begin{array}{ccc}
n & S_Q & S_{QQ}
\vspace{0.5em}\\
S_Q & S_{QQ} & S_{QQQ}
\vspace{0.5em}\\
S_{QQ} & S_{QQQ} & S_{QQQQ}
\end{array}
\right]
\left[
\begin{array}{c}
a
\vspace{0.5em}\\
b
\vspace{0.5em}\\
c
\end{array}
\right]
=
\left[
\begin{array}{c}
S_P
\vspace{0.5em}\\
S_{PQ}
\vspace{0.5em}\\
S_{PQQ}
\end{array}
\right]