Copper sulfate from a processed ore containing inert solids and copper sulfate is extracted with pure water in a countercurrent multistage extraction system. The ore to be extracted contains 9000kg/h inert solids (B), 1000kg/hr copper sulfate (A) and 400kg/hr water (C). 95% of the copper sulfate in the ore is desired to be recovered. The outlet of the overflow solution contains 90% water and 10% copper sulfate. The value of N for the slurry underflow is kept constant at N=0.5kg inert solid/ kg solution. Find the exit flow rate of the underflow after leaching