Assume that the ship is all-inclusive, and there are 8X6=48 people.

Now there are 38 people, so there are 48-38 more people =10.

Every time a boat is added, two people are missing, so the number of boats is 10÷2=5.

The number of big ships is 8-5=3.

Generally speaking, the formula is the number of ships (8X6-38)÷(6-4)=5.

Number of large ships 8-5=3