# If $A=\begin{bmatrix}1 & 5\\7 & 12\end{bmatrix}\;and\;B=\begin{bmatrix}9 & 1\\7 & 8\end{bmatrix},$ find a matrix $C$ such that $3A+5B+2C$ is a null matrix.
$\begin{array}{1 1} C=\begin{bmatrix}-4 & 0\\-28 & -38\end{bmatrix} \\ C=\begin{bmatrix}-24 & -10\\-28 & -38\end{bmatrix} \\ C=\begin{bmatrix}24 & 10\\28 & 38\end{bmatrix} \\ C=\begin{bmatrix}-2 & -10\\-28 & -38\end{bmatrix} \end{array}$