Answer from textbook is 87 m^2, but I am not sure how to get that.

17.22. Heat-transfer area of a cooling crystallizer. Feed to a cooling crystallizer is 2,000 kg/h of 30 wt% Na2SO4 in water at 40C. This solution is to be cooled to a temperature at which 50% of the solute crystallizes as decahydrate. Estimate the required heat-transfer area in m2 if an overall heat-transfer coefficient of 15 Btu/h-ft--F can be achieved. Assume a constant specific heat for the solution of 0.80 cal/g-C. Cooling water at 10C flows countercurrently to the solution, and exits at a tempera- ture that gives a log mean driving force of at least 10C