A 200 kg batch of granular solids containing 30 per cent of moisture is to be dried in a tray dryer to 15.5% moisture by passing a current of air at 350 K tangentially across its surface at the velocity of 1.8 m/s. If the constant rate of drying under these conditions is 0.7 g/sm2 and the critical moisture content is 15%, calculate the approximate drying time. It may be assumed that the drying surface is 0.03 m2/kg dry mass