Answer
$\begin{bmatrix} -20 &0\\16&-6\end{bmatrix} $
Work Step by Step
When we multiply a scalar $k$ with a matrix $A$, then the product will be the matrix $kA$, each of whose elements is $k$ times the corresponding element of $A$.
Our aim is to compute $-2A+4B$, for this we will multiply each element of the matrix $A$ by $-2$ and every element of $B$ by $4$, then add them .
Therefore, we have:
\begin{align*}
-2A+4B&= -2 \begin{bmatrix} -2 &4\\0&3\end{bmatrix} +4 \begin{bmatrix} -6 &2\\4&0\end{bmatrix}\\ \\&=\begin{bmatrix} 4 &-8\\0&-6\end{bmatrix} +\begin{bmatrix} -24 &8\\16&0\end{bmatrix} \\
\\&=\begin{bmatrix} 4-24 \quad&-8+8\\0+16\quad&-6+0\end{bmatrix}\\
\\&=\begin{bmatrix} -20 &0\\16&-6\end{bmatrix}
\end{align*}
