Science and technology book: 1680×45%=756 (Ben),

Comics: 1680×25%=420 (Ben),

A: There are 504 story books, 756 science books and 420 comic books.

(2)756-504=252 (Ben),

504-420=84 (Ben),

Answer: There are 252 storybooks less than science books and 84 comic books less than storybooks.

(3) Number of storybooks: number of comic books = 504: 420 = 6: 5,

A: The ratio of storybooks to comic books is 6: 5.