Membranes represent a relatively new technology for the separation of gases. One use that is being studied is the separation of nitrogen and oxygen from air. $100$mol$\frac{e}{m}in$ of air is fed to a membrane which produced two streams, permeate $($product$)$ and retentate $($waste$)$ streams. The permeate stream account for $20\%$ of the feed and has oxygen concentration of $25$mole$\%.$ Calculate the flow rate of permeate and retentate stream in mole$/$ min, and the mass fraction of oxygen in the retentate stream.