Consider, pls, this solution.
Note, that V1 marked with orange lines (see the graph), V2 - with green colour.
Using a Laplace expansion along the first column, we have

The determinant of a 2x2 matrix is trivial,

So we have

Answer: (C) 4
<u>Step-by-step explanation:</u>
The corresponding sides of a 30°-60°-90° triangle are: b - b√3 - 2b
The side corresponding to 90° is 8 = 2b --> b = 4
The side corresponding to 30° is y = b <em>as stated above, b = 4</em>, so y = 4