47. An average family of four uses roughly 1200 L (about 300 gallons) of water per day (l L = 1000 cm3). How much depth would a lake lose per year if it uniformly covered an area of 50 km2 and supplied a local town with a population of 40,000 people?

 47. An average family of four uses roughly 1200 L (about 300 gallons) of water per day (l L = 1000 cm3). How much depth would a lake lose per year if it uniformly covered an area of 50 km2 and supplied a local town with a population of 40,000 people? Consider only population uses, and neglect evaporation and so on.