The question in the book is in the chapter on Conservation of Momentum and elastic/inelastic collision equations are later within the book. I believe they are trying to make it as simple as possible without overcomplicating the question as more complex equations involving the conversation of...
I actually contacted the company who published this question in their book and it has been reviewed. They sent me the correct information for the question as it was an error in printing and will be corrected in future printed copies. The question should read as follows.
"On the given pool...