Find parametric equations for the surface obtained by rotating the curve $y = 9 x^4 -x^2, -3 \leq x \leq 3$ about the x-axis, and use them to graph the surface.
$\mathbf{r}(s, t) = \langle s,$ , $\rangle$
$\leq s \leq$
$\leq t \leq$