Consider a village in which everybody can drink tap water. However, after a strong rainy days, the tap water was polluted with an octamethyltetrasiloxane (D4) substance at a concentration 10 ppm. Consider that there is a flow rate of fresh water (F: 105 L day ¹) into the tap water stream that equals the rate at which water leaches into the pollutant. The volume of this area is 107 L. Drinking water from the tap will be safe only once concentration of D4 is lower than 5 ppm. After how many days can the villagers be able to drink tap water safely? (1 ppm is equivalent to 1 mg/L)