Earth-whose in situ weight is 112 lb/cf, whose loose weight is 95 lb/cf, and whose compacted weight is 120 lb/cf-is placed in a fill at the rate of 250 cy/hr, measured as compacted earth. The thickness of the compacted layers is 6 in. A compactor with a roller drum width of 84 in. is used to compact the material at a speed of 2.5 mph. Assume a 55-min hour operating efficiency. Determine the number of rollers required to provide the necessary compaction rate if eight drum passes are specified for each layer of earth.