A continuous disc-stack centrifuge is operated at 4000 rpm for separation of bakers' yeast. At a feed rate of 60 l/min, 50% of the cells are recovered. At constant centrifuge speed, solids recovery is inversely proportional to flow rate. What flow rate is required to achieve 90% cell recovery if the centrifuge speed is maintained at 4000 rpm and what operating speed is required to achieve 90% recovery at a feud rate of 40 V/min