Which equations would help us find out how many shelves are on the bookcase

There are 45 books on the bookcase in Riya's bedroom. Each shelf on the bookcase has 9 books.
Which equations would help us find out how many shelves are on the bookcase?
Choose 2 answers:
A. 9÷45=?
B. 45÷9=?
C. 9×45=?
D. 9×?=45