Hexachlorobiphenyls, a type of PCB$,$ decays in the environment as a first$-$order reaction with a rate constant of $\frac{0\mathrm{.}31}{?}$ day.

A$.$ Waste containing hexachlorobiphenyls is dumped into a pond. How long $($in days$)$ will it take for $99\mathrm{.}99\%$ of the initial concentration to decay?

B$.$ Waste containing $50ppm$ hexachlorobiphenyls is dumped into a completely$-$mixed lake in a flowrate of $5\frac{m^3}{?}$ day. Several streams containing no hexachlorobiphenyl enter and leave the lake with a total flowrate of $300,000\frac{L}{?}$ day. If the hydraulic retention time of the lake is $100$ days, what is the concentration of hexachlorobiphenyl in the lake at steady state?