a vessel contains 7000 kg of an ethanol/water solution at a concentration of 4%. an upstream reaction will feed a constant flowrate of 1000 kg/h of ethanol solution at a concentration of 7% into the tank. At the same time, a withdrawal of 800 kg/h of the solution will begin. Assuming that these flow rates remain constant for the next week and that the volume of the tank is very large, derive an expression for the ethanol concentration leaving the tank, and determine the time it takes for the concentration to reach 5% ethanol