[填空题]
$\text { Let } f(x)=x(x-3)^{2} \text {, for } 0 \leq x \leq 4 \text {. The following graph shows } f \text {. }$
Let R be the region enclosed by the x -axis and the curve of f .
1. Find the area of R .
2. Find the volume of the solid formed when R is rotated $360^{\circ}$ about the x -axis.
3. The diagram below shows part of the graph of the quadric function g(x)=x(a-x) . The graph of g crosses the x -axis when x=a .
The area enclosed by the graph of g is equal to the area of R . Find the value of a .
