Consider the diffusion of dopant element A into crystalline water. The dopant rich coating is considered as a large source of A relevant to the amount of A diffused, so that the surface concentration CAs can be considered a constant. Determine the depth (z) of the front of diffusing dopant after two hours of diffusion. Assume that the front concentration is 2% of the surface concentration. Diffusivity of A= 6.5 X 10^-13 cm^2/s.