$1.$ A standard five$-$day BOD test is run using a mix consisting of four parts distilled water $($no organics or seed in the distilled water$)$ and one part wastewater. The initial DO of the mix is $\backslash (9\mathrm{.}0\backslash$mathrm$\{$mg$\}/\backslash$mathrm$\{$L$\}\backslash ),$ and the DO after five days is determined to be $\backslash (2\mathrm{.}0\backslash$mathrm$\{$mg$\}/\backslash$mathrm$\{$L$\}\backslash ).$ What is the $\backslash ($ B O D$\_\{5\}\backslash )$ of the wastewater sample?

$2.$ The following data have been obtained in a BOD test that is made to determine how well a wastewater treatment plant is operating:

What percentage of the $\backslash (\backslash$mathrm$\{$BOD$\}\_\{5\}\backslash )$ is being removed by this treatment plant? If this is a treatment plant that is supposed to remove $85$ percent of the $\backslash (\backslash$mathrm$\{$BOD$\}\_\{5\}\backslash ),$ would you say it is operating properly?