mass-transfer problem

The patch for delivering the drug through the skin contains 0.06 M of drug solution in a capsule with a thickness of 2 mm and a diameter of 3 cm. Before attaching this, a 250 m thick polymer membrane was placed between the capsule and the skin. The diffusion coefficient of the drug in the solution is 5.4 x 10^-6 cm²/sec, and the diffusion coefficient in the polymer is 1.8 x 10^-7 cm²/sec. The equilibrium concentration in the polymer phase is 0.6 times the equilibrium concentration in the solution. It is assumed that the drug is absorbed quickly by the skin, and the concentration at the polymer-skin interface is zero. (a) How much is the drug in the capsule absorbed in the first 2 hours? (b) When does the discharge rate of the drug become half the initial rate? How many moles have been discharged by that time? (c) Can you suggest a way to ensure that the drug is discharged at a nearly constant rate?