Problem

甲、填充題：共 8 題，每題 8 分，共 64 分。請在答案卷上列出題號依序作答。

6. Find the volume of the solid obtained by revolving the region bounded by the curves $y=-x^2+4x$ and $y=x^2$ about the $x$-axis. Answer : \underline{\quad(1)\quad}