$.$ Consider the steady$-$state diffusion of a protein across a tissue that consists of two phases

$($a cellular phase and an acellular phase$).$ This tissue can be described as a two$-$layer laminate as shown in the

figure below. The two layers have thicknesses of $L_1$ and $L_2,$ respectively $(L=L_1+L_2).$ The protein has

separate diffusion coefficients in the two phases $(D_1$ and $D_2,$ respectively$).$ Treat each phase as homogenous,

each with a single, nonzero partition coefficient $({}_1$ and ${}_2,$ respectively$).$ The concentration of the protein at

$x=0$ is $C_0,$ and the concentration is $C_L$ at $x=L.$ Assume no reactions take place.

Find expressions for the concentration of the protein in each layer, $C_1(x)$ and $C_2(x).$ Also, find the flux of

protein through each layer and $\{$:$N_{2x}).$