ANSWER TO QUESTION THREE: SMALL BLUE BOX
This question is a little harder than the others, because there are no drawings. To make this easier, you can draw a 3×3 table where the columns are red, black, and blue, and the rows are small, medium, and large. Possible boxes marked with an X will thus look like this;
If Caroline doesn’t know the box, the answer cannot be ‘black’. If she knew that Susan didn’t know, Caroline couldn’t have been told ‘red’ either, because if she had been told ‘red’ then there’s a good chance that Susan would have been called ‘medium’, in which case Caroline wouldn’t have said it.
To be able to say that Susan knows that she doesn’t. It shows Caroline being called ‘blue’. Now, if Susan knows before Caroline speaks that Caroline doesn’t know the right box, we can rule out the possibility that Susan was told “big”. If he had been called ‘big’, he wouldn’t have known for certain that Caroline didn’t. Since the box is blue and not large, the only remaining options are small and blue.