On a shelf, books with white cover and that with orange cover are in the ratio 12 ∶ 21. If there are 945 books with orange cover, then the number of books with white cover is:
1
540
2
840
3
645
4
1485
On a shelf, books with white cover and that with orange cover are in the ratio 12 ∶ 21. If there are 945 books with orange cover, then the number of books with white cover is: