The problem I'm working on is...

A truck gets 500/x

miles per gallon (mpg) when driven at a constant speed ofx mph, where 40 ≤ x ≤ 80.I have been searching for similar problems in my text book and class notes but am unable to find one. I'd greatly appreciate any help or similar examples!

If the price of fuel is $2.80/gal and the driver is paid $20/hr, at what speed is it most economical for the trucker to drive?

Thanks!