overall transfer units

Water is to be cooled at the rate of 10 kg/s from 317 K to 300 K in a countercurrent cooling tower under conditions such that Htoc = 2.5 m. Air enters at the bottom of the tower at 297 K and a wet-bulb temperature of 294 K. The air rate to be used is 1.33 times the minimum.
(a) Using the results of Problem 8.6, calculate the minimum air rate.
(b) For the specified airflow rate [1.33Vs’(min)], calculate the number of overall transfer units and tower packed height.