Answer
$40$
Work Step by Step
The determinant $D$ of a $ 2 \times 2$ matrix can be calculated as:
$D=\left|\begin{array}{ll}
A & B\\C & D \end{array}\right|=AD-BC$
The determinant $D$ of a given $ 2 \times 2$ matrix can be calculated as:
$D=\left|\begin{array}{ll}
-9 & 7\\ 2 & 6 \end{array}\right|=(-9)(6)-(7)(2)=54-14=40$
