Assume that the operating cost of a certain truck (excluding driver's wages) is 12+x/6 cents per mile when the truck travels at x mi/hr. if the driver earns $6 per hour, what is the most economical speed to operate the truck on a 400 mi turnpike where the minimum speed is 40 mph and the maximum speed is 70 mph?

Explanation:

Given that the operating cost is

cents per mile

total miles covered is given as

so total cost of drive is given as

$

time taken by the truck to move the distance is given as

So total earnings of the driver is given as

$

now total profit of the driver is given as

$

to maximize the profit we have

so we have

i don't know that i agree with that but what's the question ?