Why does time seem to flow only in one direction?

An airplane travels from st. louis to portland, oregon in 4.33 hours. if the distance traveled is 2,742 kilometers. what is the airplane's average speed? - the airplane returns to st. louis by the same route. because the prevailing winds push the airplane along, the return trip takes only 3.75 hours. what is the average speed for this trip? - the airplane refuels in st. louis and continues on to boston. it travels at an average speed of 610 km/h. if the trip takes 3.75 hours. what is the flight distance between st. louis and boston?