Answer
$\begin{bmatrix} -3 \\ 10 \end{bmatrix}$
Work Step by Step
We can see the number of columns in first matrix is same as number of rows of a second matrix, so their product is possible.
$D= \begin{bmatrix} 1 & -2 & 4 & 2\\ 0& 1 &-1&8 \end{bmatrix} \begin{bmatrix} -1\\ 2\\0 \\1 \end{bmatrix}\\=\begin{bmatrix} -1-4+0+2 \\ 2+8 \end{bmatrix}\\=\begin{bmatrix} -3 \\ 10 \end{bmatrix}$
