Step-by-step explanation:
we start with finding how many gallons of their fuel they will need for the trip:
the gas version gets 29 miles per gallon. for 500 miles that is 500/29 = 17.24137931... gallons
the diesel version gets 33 miles per gallon. for 500 miles that is 500/33 = 15.15151515... gallons.
now we multiply the needed gallons by their price.
17.24137931... gallons of gas cost
17.24137931... × 2.3 = $39.65517241...
15.15151515... gallons of diesel cost
15.15151515... × 2.5 = $37.87878788...
so, the diesel vehicle is the cheaper version for the trip.