$20$ Points. Consider diffusion of a drug across a two$-$layer membrane mounted in between two compartments $($donor and receiver$)$ of a diffusion cell. Layer $1$ in contact with the donor side is $0\mathrm{.}1$ mm thick and Layer $2$ in contact with the receiver size is $0\mathrm{.}3$ mm thick. The diffusion coefficient of the drug in Layer $1$ is $0\mathrm{.}2\backslash$times $1010$ m$2/$s and in Layer $2$ is $0\mathrm{.}1\backslash$times $1010$ m$2/$s$.$ The partition coefficient of the drug in

Layer$1$ and Layer $2$ are $10$ and $50,$ both with respect of concentration in water. The concentration in the donor and receiver chambers are fixed at $5$ mg$/$mL and zero, respectively. Calculate the flux of drug from the donor to the receiver chamber.