Multiplying a matrix by a scalar is equivalent to multiplying each entry in the matrix by that scalar:
[tex]A=\begin{bmatrix}0&-3\\-5&5\end{bmatrix}\implies3A=\begin{bmatrix}0&-9\\-15&15\end{bmatrix}[/tex]
[tex]B=\begin{bmatrix}-2&-6\\2&5\end{bmatrix}\implies-6B=\begin{bmatrix}12&36\\-12&-30\end{bmatrix}[/tex]
Now combine them:
[tex]3A-6B=3A+(-6B)=\begin{bmatrix}0+12&-9+36\\-15+(-12)&15+(-30)\end{bmatrix}=\begin{bmatrix}12&27\\-27&-15\end{bmatrix}[/tex]
