A 500L tank initially haves 300 L of fluid on which there is dissolved 50 grams of sulfuric acid. Fluid having 30 grams per liter of sulfuric acid flows in the tank at the rate of 4 liters per minute. the mixture is kept uniform by stirring. and the stirred mixture simultaneously flows out of the tank at a rate of 2.5 liters per minute. How much of sulfuric acid is in the tank at the instant it overflows?