Drying of Wood. A flat slab of Douglas fir wood $50\mathrm{.}8$ mm thick containing $30$ wt $\%$ moisture is being dried from both sides $($neglecting ends and edges$).$ The equilibrium moisture content at the surface of the wood due to the drying air blown over it is held at $5$ wt $\%$ moisture. The drying can be assumed to be represented by a diffusivity of $3\mathrm{.}72*10^-6$ m$^2/$h$.$ Calculate the time for the center to reach $10\%$ moisture