I can't buy the Japanese textbook because it's too expensive.
Please don't share the textbook. Each person must buy their own.
I forgot to bring my textbook and I was kept an hour after school.
The thing you use to teach a course with writings is a textbook. It's a book of writings you use to teach your course!
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.