A 75 mm thick wooden plate contains 2.8 % by mass water, relative to dry wood, which corresponds to a mass fraction of ξA α = XXXXXXXXXXAt equilibrium with the environment the mass fraction is reduced...

A 75 mm thick wooden plate contains 2.8 % by mass water, relative to dry wood, which corresponds to a mass fraction of ξA_α
= 0.218. At equilibrium with the environment the mass fraction is reduced to ξA_S
= 0.065.

How long does it take for the mass fraction of water in the middle of the plate to fall to ξA(x = 0) = 0.08? The diffusion coefficient of water in wood is D = 1.2 · 10⁻⁹
m²/s.