Comparing Design Strengths Practice Test

Amir and Maya study container tests. Design A was one box, and items got mixed (yes). Design B had dividers, and items stayed separated (yes). They use the data to find strengths and weaknesses. From the testing, why are dividers a strength in Design B?

Yuki and Carlos look at shelf tests for storing books. Design A (one shelf): holds 8 books. Design B (three shelves): holds 24 books. They say more books held means it works well for storage. Based on the data, which design holds more books?