英文数学题,求高手,急
Atruckgets
500/x
milespergallon(mpg)whendrivenataconstantspeedofxmph,where
40≤x≤80.Ifthepriceoffuelis$2.80/galandthedriverispaid$17/hr,atwhatspeedisitmosteconomicalforthetruckertodrive?(Roundyouranswertotwodecimalplaces.)