Answer:
18 divided by 2/9, or 18/(2/9) (Is this what the first option was meant to say?)
Step-by-step explanation:
18 inches is the amount of space that needs to be filled, or divided up into sections to see how many things can fit.
2/9 is the width of the thing that you need to see how many fit, meaning it's the thing you're dividing by.
Combined, this means your expression is 18 divided by 2/9, or 18/(2/9). I think this is what your first option was meant to say, because if it is what it says, then the first and second option would be the exact same wrong thing.
You DON'T multiply, because if you think about easy numbers, an inch thick book should have 18 fit, and a half-inch thick book should have double that fit. As you get a smaller book, the number that fit increase, which can't happen with multiplication.
You also don't start with 2/9 because that's the width of the book. You're not trying to see how many boxes can fit into each book; that'd be ridiculous.
