A chemical is added at the beginning of a water treatment plant at a dose of 750 lb/day. The water treatment plant provides water to a community of 200,000 people and the average water consumption in the city is 110 gallons per capita per day (gpcd). If 10% of the chemical remains following reactions (i.e., 90% of the added chemical reacts following addition), find the residual chemical concentration (in mg/L) and the amount of chemical that was required for the reaction (in mg/L).