Evaluate the expression LaTeX: \displaystyle 3 A - 7 B - 3 C
LaTeX: A = \left[\begin{matrix}3 & -7\\1 & 6\\2 & 1\\5 & 4\end{matrix}\right],\quad\quad B = \left[\begin{matrix}4 & -9\\5 & 5\\2 & -5\\4 & -7\end{matrix}\right], \text{ and } \quad C = \left[\begin{matrix}4 & 7\\5 & 4\\1 & -4\\4 & -6\end{matrix}\right].

The sum is LaTeX: \displaystyle \left[\begin{matrix}-31 & 21\\-47 & -29\\-11 & 50\\-25 & 79\end{matrix}\right] .