A $12.0\mathrm{mL}$ portion of waste water is made up to $300\mathrm{mL}$ with oxygen-saturated dilution water. The diluted mixture has dissolved oxygen of $8.7\mathrm{mg}{\mathrm{L}}^{-1}$ at the start and $4.9\mathrm{mg}{\mathrm{L}}^{-1}$ after incubation for 5 days at 20 ${}^{\circ }$C. The BOD${}_5$ of the original waste water is calculated as (initial DO minus final DO) times the dilution factor. Give the BOD${}_5$ in $\mathrm{mg}{\mathrm{L}}^{-1}$ to the nearest integer.

Numerical answer type, answer in mg/L, tolerance 0.5.