Answer: 12.8%
Step-by-step explanation: To find the part of all books that are science books, we need to calculate the ratio of science books to the total number of books. The total number of books is the sum of the art books and the science books, which is 65,400 + 9,600 = 75,000 books.To find the part that are science books, we divide the number of science books by the total number of books and then multiply by 100 to get the percentage. So, the part of all books that are science books is (9,600 / 75,000) * 100 = 12.8%.Therefore, approximately 12.8% of all books in the library are science books.