TeX source:

\begin{aligned}\mathrm{C} &=\text { total welding cost }=(\text { top seam } \mathrm{cost})+(\text { bottom seam cost })+(\text { side seam cost }) \\&=(\text { top seam length }) \cdot(80 ¢ / \text { inch })+(\text { bottom seam length }) \cdot(80 ¢ / \mathrm{in})+(\text { side seam length }) \cdot(80 ¢ / \mathrm{in}) \\&=(2 \pi \mathrm{r}) \cdot(80)+(2 \pi \mathrm{r}) \cdot(80)+(\mathrm{h}) \cdot(80)=320 \pi \mathrm{r}+80 \mathrm{~h} .\end{aligned}