Answer
$29$
Work Step by Step
For any matrix \[
\left[ {\begin{array}{cc}
a & b \\
c & d \\
\end{array} } \right]
\] the determinant equals $ad-bc$. For the matrix \[
\left[ {\begin{array}{cc}
9 & -8 \\
-7 & -3 \\
\end{array} } \right]
\] the determinant equals $9(-3)-(-7)(-8)=29.$