1. What's your favorite class?
2. It's math.
3. It's math class.
4. It's a math class.
5. My favorite class is math.
Which are the right answers for the question?
6. What's your favorite subject?
7. It's math.
(What about the question, #6? Is the question the same as question 1 or different one?)
All of the answers are correct.
Numbers 1 and 6 are nearly the same. Number 1 implies a class you're taking now. Number 6 could be any class -- one you're taking now or one you took a couple of years ago.
The right answers for the question "What's your favorite class?" are 2, 3, 4, and 5. Each of these responses explicitly states that the favorite class is math. You can determine this by looking for the phrase "It's math" or "My favorite class is math" in the answer.
Regarding question #6, "What's your favorite subject?" is a different question from question #1, which asks about favorite class. While the topics are related, subjects can be broader and encompass multiple classes. In this case, the response to question #6 would be answer 7, "It's math."