A tank initially haves 1000 liters of pure water. Then water containing 5 mg of detergent per liter starts to enter tank at rate of 10 liters per hour
a) How long till the average concentration of detergent in the tank is 2 mg per liter?
b) How long until the average concentration of detergent in the tank is x mg per liter?
c) What does your answer to part (b) give when x = 7.