Two ton/h of the dodecahydrate of sodium phosphate (Na₃PO₄ · 12H₂O) is to be crystallized by cooling, in a cooling crystallizer, an aqueous solution that enters saturated at 40°C and leaves at 20°C. Chilled cooling water flows countercurrent, entering at 10C and exiting at 25C. The overall heat-transfer coefficient is 20 Btu/h-ft²-F. Solution average
specific heat is 0.80 cal/g-C. Estimate the: 

(a) Tons (2,000 lb) per hour of feed solution; 

(b) Heat-transfer area in ft²; 

(c) Number of crystallizer units required if each 10-ft-long unit contains 30 ft² of heat-transfer surface.