Answer
$6$.
Work Step by Step
The given determinant is a second order determinant.
$A=\begin{vmatrix}
a &b \\ c & d
\end{vmatrix}$
Its value is calculated with the formula:
$det A=ad-bc$.
Cross multiply and subtract as shown above in order to calculate the value of the given determinant.
$\begin{vmatrix}
-2 &-4 \\ 5
& 7
\end{vmatrix}=(-2)(7)-(5)(-4)$
Simplify.
$=-14+20$
$=6$.
