Answer
$\begin{bmatrix} -1 &-3\\2&-3\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 $-A+\dfrac{1}{2}B$, for this we will multiply each element of the matrix $A$ by $-1$ and every element of $B$ by $\dfrac{1}{2}$ , then add them .
Therefore, we have:
\begin{align*}
-A+\frac{1}{2}B&= - 1 \begin{bmatrix} -2 &4\\0&3\end{bmatrix} +\left(\frac{1}{2}\right) \begin{bmatrix} -6 &2\\4&0\end{bmatrix}\\
\\&=\begin{bmatrix} 2 &-4\\0&-3\end{bmatrix} +\begin{bmatrix} -3 &1\\2&0\end{bmatrix} \\
\\&=\begin{bmatrix} 2-3 \quad&-4+1\\0+2\quad&-3+0\end{bmatrix}\\
\\&=\begin{bmatrix} -1 &-3\\2&-3\end{bmatrix}
\end{align*}
