Since there are 24 fiction books and 52 books in total, you can start with subtracting them both to find the amount of non-fiction books. 52-24=28, so 28 non-fiction books are currently checked out. Now for the fun part. There are two ways I know how to do this, so let's start. One way is that you can put a ':' between the two numbers. For example, since we are trying to find fiction books to non-fiction, we would say 24:28. The first number will represent the first thing they ask for (fiction), and the second number will represent the second thing they ask for (non-fiction). Another way to do this is by putting the numbers as a fraction. For example, you could put 24/28. It will still mean the same thing, and it will not change the outcome. I hope this helps! :)