TeX source:
\mathrm{C}=9 \mathrm{wl}+10 \mathrm{lh}+10 \mathrm{wh}=9 \mathrm{w}(3 \mathrm{w})+10(3 \mathrm{w}) \mathrm{h}+10 \mathrm{wh}=27 \mathrm{w}^{2}+40 \mathrm{wh}