Answer
The answer is $ -16$.
Work Step by Step
We know that for a matrix
$\begin{bmatrix}
a & b\\
c & d
\end{bmatrix}$
the determinant is $ D=ad−bc$.
the given determinant is
$\begin{vmatrix}
4 & 8\\
5 & 6
\end{vmatrix}$
Hence, $D=4 \cdot 6-8\cdot5 =24-40=-16 $
