의문문의 화법전환문제인데요

문)
mina : do you know how many characters hangeul has?
mike : 24.
mina : good.

mina asks, _____________________
mike knows how many characters hangeul has. he says it has 24 characters.

보기
1. how many characters has hangeul?
2. how many characters hangeul does have?
3. how many characters does hangeul have?
4. how many characters does hangeul has?
5. how many does characters hangeul has?

답이 3번이라는데
명확하고쉽게설명부탁드려요ㅠㅠ