It is normal for nine-year compulsory education to have questions that cannot be done. Maybe it's too difficult, or you didn't hear what the teacher said, so you really can't find the examples in the book. If there are no books, ask your classmates or teachers, and be sure to find out how to do this problem. If there are questions that you can't do in the exam, you will only have time. Ask the teacher when you come down. After learning, you can do it. Mathematics is very important, so you must study hard.