$5\mathrm{.}3$ Earth$-$whose in situ weight is $112l\frac{b}{c}f,$ whose loose weight is $95l\frac{b}{c}f,$

and whose compacted weight is $120l\frac{b}{c}f-$ is placed in a fill at the rate of

$250c\frac{y}{h}r,$ 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 $2\mathrm{.}5$ 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.