Answer
$x=4.$
Work Step by Step
We know that for a matrix
\[
\left[\begin{array}{rrr}
a & b & c \\
d &e & f \\
g &h & i \\
\end{array} \right]
\]
the determinant, $D=a(ei-fh)-b(di-fg)+c(dh-eg).$
Hence here $D=1(1\cdot2-1\cdot(-2))-x(3\cdot2-1\cdot0)+(-2)(3\cdot(-2)-1\cdot0)=-8\\1(4)-x(6)+(-2)(-6)=-8\\4-6x+12=-8\\16-6x=-8\\-6x=-24\\x=4.$
