Compute the Determinant of the Matrix by Cofactor Expansion $\left[ \begin{array} { r r r } 4 & - 8 & 2 \\ 0 & 1 & 8 \\ 0 & 0 & - 9 \end{array} \right]$

Compute the determinant of the matrix by cofactor expansion.
- $\left[ \begin{array} { r r r } 4 & - 8 & 2 \\ 0 & 1 & 8 \\ 0 & 0 & - 9 \end{array} \right]$

A) $- 100$
B) $- 28$
C) $- 36$
D) 36