 It costs about four times as much to fly to and from Les Saintes as to make the round-trip sea journey.
It costs more to fly than to take a boat for the journey because the pilots demand a high pay.
mnli hypothesis: It costs more to fly than to take a boat for the journey because the pilots demand a high pay. premise:  It costs about four times as much to fly to and from Les Saintes as to make the round-trip sea journey.