The answer to this is B. In order to solve this, you need to divide the gallons with the square feet which means that 2,800,000 that you will divide with 500. The answer that you will get is 5600 gallons per square foot. There is a need for people to have filtered water especially at this day and age when the products that are available cannot entirely be considered clean.
There are a lot of health conditions that may arise from drinking unfiltered water. Some suffer from diarrhea but turn out fine after. Some people suffer from other more serious conditions that may cause them to become dehydrated. It is important that there is enough filter for the amount of water that needs to be cleaned.