Answer
120
Work Step by Step
Expand using the column with the most zeros:
$\begin{array}( \\|A|= \\ \\ \end{array}
\begin{vmatrix} 1 & 2&3&4 &5\\0 & 2&4&6 &8\\0 & 0&3&6 &9\\0 & 0&0&4 &8\\0 & 0&0&0 &5\end{vmatrix}\begin{array}( \\= \\ \\ \end{array}
\begin{vmatrix} 2&4&6 &8\\ 0&3&6 &9\\ 0&0&4 &8\\ 0&0&0 &5\end{vmatrix}\begin{array}( \\=(2) \\ \\ \end{array}\begin{vmatrix} 3&6 &9\\ 0&4 &8\\ 0&0 &5\end{vmatrix} \begin{array}( \\=(2)(3) \\ \\ \end{array}\begin{vmatrix} 4 &8\\ 0 &5\end{vmatrix} $
$|A|=2\times3\times4\times5=120$
