An air stream of 150 kg/h at 33 °C and a relative humidity of 20% passes through a bed of wet solids in a dryer. Measurements made on the equipment indicate that the air residence time is 18 min. The mass of the initial solid is 100 kg with a humidity of 4%. The process is isothermal and the air stream leaves saturated. Assume that the moisture from the solid is transferred to the air. Determine the final moisture of the solid.