Determinant Matrix

Find the determinant of the following 2 x 2 matrix:

Expand Hint
Hint 2
$$$\begin{bmatrix}a_{1} & a_2\\ b_1 & b_2\end{bmatrix}=(a_{1})(b_2)-(a_2)(b_1)$$$
$$$\begin{bmatrix}a_{1} & a_2\\ b_1 & b_2\end{bmatrix}=(a_{1})(b_2)-(a_2)(b_1)$$$
$$$\begin{bmatrix}1 & 5\\ 4 & 8\end{bmatrix}=(1)(8)-(4)(5)=8-20=-12$$$
-12