TRANSPORTATIONCOSTFor speeds between 40 and 65 miles per hour, a truck gets  miles per gal...

TRANSPORTATIONCOSTFor speeds between 40 and 65 miles per hour, a truck gets  miles per gallon when driven at a constant speed of x miles per hour. Diesel gasoline costs $3.90 per gallon, and the driver is paid $19.50 per hour. What is the most economical constant speed between 40 and 65 miles per hour at which to drive the truck?