Large, medium and small ships are used to bring water. 4 large ships carry as much water as 7 small ships.
3 medium ships carry the same amount of water as 2 large ships and 1 small ship.
15 large, 7 medium and 14 small ships, each made 36 journey and brought a certain quantity of water.
In how many journeys would 12 large, 14 medium and 21 small ships bring the same quantity?