On Monday, 40 of the 160 available books in a library's collection were
borrowed. On Tuesday, half of the books borrowed on Monday were returned and
on Wednesday half of the remaining borrowed books from Monday were returned.
On Thursday, the library receives 30 more available books, and a sixth of the
remaining borrowed books from Monday are returned. On Friday, 30 more books
are borrowed and on Saturday 35 more books are borrowed. If no other books
were borrowed, returned, or received during the week, what is the percent
change of the available books at the end of the day Monday to the available
books at the end of the day on Saturday?