Neco 2020 Chemistry Question 19

A factory discharges wastewater containing pollutant X at a concentration of 0.15\,mg\,L^{-1} with a flow rate of 5\,000\,L\,min^{-1}. The river into which it is released has a flow rate of 1.0\times10^{5}\,L\,min^{-1} and a background concentration of X equal to 0.005\,mg\,L^{-1}. Environmental regulations require that the concentration of X downstream of the mixing point must not exceed 0.010\,mg\,L^{-1}. The factory can install a treatment unit that reduces the concentration of X in its effluent by a percentage p (where 0\le p\le100). Assuming complete mixing and that the treatment does not change the effluent volume, calculate the minimum percentage removal p required to meet the regulatory limit.