Answer
$-44$
Work Step by Step
Since we have $$\left[\begin{array}{rrr} {4} & {2} \\ {6} & {-8}\end{array}\right]=2\left[\begin{array}{rrr} {2} & {1} \\ {3} & {-4}\end{array}\right]$$
then, we get
$$\left|\begin{array}{rrr} {4} & {2} \\ {6} & {-8}\end{array}\right|=2^2\left|\begin{array}{rrr} {2} & {1} \\ {3} & {-4}\end{array}\right|=4(-8-3)=-44.$$
