A flat slab of Douglas fir wood 50.8 mm thick containing 30 wt% moisture is being dried from both sides (neglecting edges and ends). 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 3.72 X 10-6 m2/hr. Calculate the time for the center to reach 10 wt% moisture.