Given that the water to be treated contains 10.1 mg benzidine/L and the desired treated water concentration of benzidine is 0.3 mg benzidine/L or less, determine the kilograms of Filtrasorb 400 required to treat 4x106 liters of water using: (1) one equilibrium stage contactor; (ii) two (counter-current) equilibrium stage contactors; (iii) a packed-bed column (assume that the rate of transport to and into the carbon is infinitely fast)