Answer
$\begin{bmatrix} -9 & 3\\ 10& 6 \end{bmatrix}$
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.
$D= \begin{bmatrix} 3 & 2 &-1\\ 4& 0 &6 \end{bmatrix} \begin{bmatrix} -2 & 0\\ 0& 2\\3 & 1 \end{bmatrix}\\=\begin{bmatrix} -6+0-3 & 0+4-1 \\ -8+18& 6 \end{bmatrix}\\=\begin{bmatrix} -9 & 3\\ 10& 6 \end{bmatrix}$
