3. Pure water at 26.1 °C is flowing at a velocity of 0.1 ft/h through a packed bed of 0.251-in. benzoic acid spheres having a total area of 0.129 ft². The solubility of benzoic acid in water is 0.00184 lb mol benzoic acid/ ft' solution. The outlet concentration C42 is 1.8 x 10 lb- mol/ft. Calculate the mass transfer coefficient ko.