3. For a filter going through backwash, the bed expanded by 25%. The filter uses silica sand with a density of 2.65 g/cm3. The fixed bed depth is 1.5 m and media size is 1.15 mm. The porosity is 48% and the operational temperature is 15C. Determine the backwash flow rate. Ky= 228, KI = 4.4