If 18 binders bind 900 books in 10 days, How many binders will be required to bind 660 books in 12 days?

According to given question,
Since 900 books are bonded in 10 days by 18 binders.
∴ 1 books are bonded in 10 days by 18 / 900 binders.
∴ 1 books are bonded in 1 days by 18 x 10 / 900 binders.
∴ 660 books are bonded in 1 days by 18 x 10 x 660 / 900 binders.
∴ 660 books are bonded in 12 days by 18 x 10 x 660 / 12 x 900 binders.
∴ 660 books are bonded in 12 days by 18 x 10 x 55 / 900 binders.
∴ 660 books are bonded in 12 days by 18 x 55 / 90 binders.
∴ 660 books are bonded in 12 days by 55 / 5 binders.
∴ 660 books are bonded in 12 days by 11 binders.