One copy is: 630÷9=70 (Ben)

The book in the lower grade is: 70×2= 140 (this book).

The mid-range book is: 70×3=2 10 (the book).

The book of senior three is: 70×4=280 (volumes).

A: The number of books distributed in lower grades is140; The number of books in the middle grade is 210; There are 280 books for senior students.