If A and B are square matrices

Given: 
A and B are square matrices of order 3
|A| = –2
|B| = 4

Now,

$|2 A B|=|2 A||B| \quad(\because|A B|=|A||B|$, if they are square matrices of same order $)$

$=|2 A| \times 4 \quad(\because|B|=4)$

$=2^{3}|A| \times 4 \quad(\because$ Order of $A$ is $3 \times 3)$

$=32|A|$

$=32 \times(-2) \quad(\because|A|=-2)$

$=-64$

Hence, $|2 A B|=-64$.