2. A rapid sand filter plant is to produce a maximum flow of 23,000 m³/day. The nominal filtration rate is 120 m/day and is not to exceed 180 m/day with one filter being backwashing nor 240 m/day with one filter being backwashing and one filter out of service. Determine the number of units required and the individual filter area. How much water is required to wash one filter if the backwash rate is 1 m/min and the duration is 10 min?