mass velocity

A gas stream flows at the rate of 10.0 m3/s at 300 K and 102 kPa. It consists of an equimolar mixture of ammonia and air. The gas enters through the bottom of a packed-bed gas absorber, where it flows countercurrent to a stream of pure liquid water that absorbs 95% of all of the ammonia, and virtually no air. The absorber vessel is cylindrical with an internal diameter of 2.2m.
(a) Neglecting the evaporation of water, calculate the ammonia mol fraction in the gas leaving the absorber.
(b) Calculate the outlet gas mass velocity (defined as mass flow rate per unit empty tube cross-sectional area)