Atruck weighs 17,000 lbs when it's trailer is empty, it gets 8 miles per gallon. it picks up 7.5 metric tons and travels 57 miles on flat ground and 20 miles at an 2.5% incline. the trucks mpg efficiency is reduced by 2.5, of the original mpg with no cargo, for every 1% incline that the truck travels. the first 9 metric tons of cargo reduces the mpg efficiency by 0.25%. what were the miles per gallon achieved by the truck?