Urgent solution required

Develop a mathematical expression for the effective mass transfer rate achieved by an implanted drug delivery device that consists of a spherical core of radius R0 containing the drug, surrounded by a gel barrier of uniform thickness (R1R0), i.e., the radius of the device (reservoir + barrier) is R1. When implanted, a scar tissue layer of thickness (R2R1) forms around the device. State and justify any assumptions you might make. For a spherical shell, the flux and mass transfer rate are given by the following expressions (see notes "Steady State Molecular Diffusion: Geometry Effects"). NA=(R11R21)DAB(CA1CA2)r21M=(R11R21)4DAB(CA1CA2)