Sounds like a some kind of object like a pencil case or chalk case (wooden, hollow) that is unique to the particular classroom where the question was asked. Making the whole thing rather silly. ;)
It's page 15 from a Mcgraw-Hill science workbook.
But I agree, it is rather silly.
Good grief! If Mr. Jeeves can't answer the question how is a kid supposed to figure it out. :^)
Could this be the answer? It can't be determined from this information. ???