a) A stream containing 10% species A by weight starts to flow at a rate of 2" " kg/min into a tank originally holding 300" " kg of pure B. Simultaneously, a valve at the bottom of the tank is opened and the tank contents are withdrawn at a rate of 2" " kg/min. Considering perfect mixing within the tank, determine the time required for the exit stream to contain 5% species A by weight ( 10 points). b) Consider the problem in part (a). As a result of malfunctioning of the exit valve, tank contents are withdrawn at a rate of 2.5" " kg/min instead of 2" " kg/min. How long does it take for the exit stream to contain 5% species A in this case? (15 points)