GATE 1997 question on Determinants

The determinant of the following matrix is :

$\begin{bmatrix} 6 & -8 & 1 & 1\\ 0 & 2 & 4 & 6\\ 0 & 0 & 4 & 8\\ 0 & 0 & 0 & -1\end{bmatrix}$

(A) 11

(B) -48

(C) 0

(D) -24

Things you need to know

If A is an upper triangular matrix, then det(A) =  Product of diagonal elements

Therefore,

Determinant = 6*2*4*(-1) = -48

Ans (B)