Please solve in detail of mass transfer

0.025m thick porous slab initially containg 0.5kg of solute A/kg of solid is placed in a well-agitated tank of Liquid B. Dereriwine the time required for the solute content at the center of the shab to decrease to 0.005kg of A/kg of solid. Neglect the counter diffussm of B into the solid. Deff =51010m/s