Answer
$-12$
Work Step by Step
Since the matrix is triangular, then one can see easily that the determinant is given by
$$(4)(1/2)(3)(-2)=-12.$$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.