Answer
$-17$
Work Step by Step
The general formula to calculate the determinate of a $2 \times 2$ matrix which has 2 rows and 2 coulmns is
$D=\begin{vmatrix}a&b\\c&d\end{vmatrix}=ad-bc$
Now,
$D=\begin{vmatrix}7&9\\-2&-5\end{vmatrix}=-35+18=-17$
