答案：(a) $40320$ (b) $8640$
- 所求的數目
$\begin{array}{cl}
= & 8! \\
= & 40320
\end{array}$ - 所求的數目
$\begin{array}{cl}
= & P^4_2 \times 6! \\
= & 8640
\end{array}$
