From a production analysis for using scrapers to move earth on a

project, the following has been determined:

The cost to operate a scraper is $$186$ per hour and to operate the push

tractor is $$145$ per hour. To achieve the $3\%$ rolling resistance $($RR$),$ it

will be necessary to add a grader to the equipment spread. A grader

costs $$120$ per hour. Calculate the cost to move a bcy of material for

all of the conditions.

a$.$ For the $4\%$ RR condition, is it better to use five or six scrapers?

b$.$ For the $3\%$ RR condition, is it better to use four or five scrapers?

c$.$ Is it economical to invest in the grader and improve production?