In a tubular steam-water type heat exchanger, the dry and saturated water vapor whose pressure is P=3.5x105 Pa, condenses on the outer surface of the tubes. The water flowing through the tubes is heated from 20 C to 90 C. Decide: A) The logarithmic average temperature difference of the heat exchanger B) The cost of steam in the steam-water exchanger if the water flow rate is 8 L/h. Assume that there is no subcooling of the condensate.