$7.)$ A project requires $2\mathrm{.}42$ million BCY of common earth material to be excavated with a $5-$

cy front shovel. The material will be loaded into $21-cy,$ loose measure articulated trucks,

and hauled $4$ miles to a fill site. The trucks will average $21$mphloaded, and $35mph$ empty.

The front shovel can excavate the common earth material at the optimum depth of cut and

at $75$ average angle of swing. It will cost $$5500$ to transport the shovel to the job, set it up$,$

and return it to the storage yard. Determine the most economical number of trucks to use

that minimizes cost. Estimate the total cost and the cost per cubic yard, bank measure, for

excavating and hauling earth. Assume the shovel and trucks will operate at a $50-mi\frac{n}{h}r$

efficiency. The following cost information applies: