Answer
$10$
Work Step by Step
The determinant for a 3 by 3 matrix can be computed as: $Determinant (D)= \begin{vmatrix} A & B & C \\
a & b & c \\
g &h & i \\ \end{vmatrix}=A(ei-fh)-B(di-fg)+C(dh-eg)$
Therefore, $D=3 [(-1) (-2) -(5)(2)]-4[1-(-2)-(5)(1)]+2[(1)(2)-(-1)(1)]\\=(3)(-8) -(4)(-7)+(2)(3) \\=-24+28+6 \\=10$