1. What is Ling-Ling not good at?

Question

2. What isn't Ling-Ling good at?

3. Why don't you like apples?
4. Why do you not like apples?

5. Why can't you solve the problem?
6. Why can you not solve the problem?
------------------
Are they all grammatical? Which expressions are commonly used?

Answer 1

All are correct ... and all are used interchangeably!