I assume you mean, (but maybe you are supposed to do something different.) .....
\(\begin{bmatrix} 7 && -6 \\ 3 && -4 \end{bmatrix} \begin{bmatrix} 3\\ -1 \end{bmatrix} = \begin{bmatrix} 7*3+-6*-1 \\ 3*3+-4*-1 \end{bmatrix} =\begin{bmatrix} 27 \\ 13 \end{bmatrix} \)
