[填空题]
$\text { A closed cylindrical can with radius } r \mathrm{~cm} \text { and height } h \mathrm{~cm} \text { has a volume of } 24 \pi \mathrm{cm}^{3} \text {. }$
1. Express h in terms of r .
The material for the base and top of the can costs 15 cents per $\mathrm{cm}^{2}$ and the material for the curved side costs 10 cents per $\mathrm{cm}^{2}$ . The total cost of the material, in cents, is C .
2. Show that C=30 $\pi r^{2}+\frac{480 \pi}{r}$ .
3. Given that there is a minimum value for C , find this minimum value in terms of $\pi$ .
