The library case study described above in Problem $1$ is extended to include the fact that the library has a significant stock of books that are no longer suitable for loaning out. These books can be sold for a fraction of the original cost. However, not all library books are eventually sold, as many are considered too damaged to sell or are simply lost or stolen. Each book copy suitable for selling has a price and the date that the book is no longer to be loaned out. Introduce enhanced concepts into the ER model you developed for Problem $1$ to accommodate this extension to the original case study.