The Hound of the Baskervilles
What is this problem and solution of chapter 15?
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This is when we find out all the information and how it was solved. Rather than writing the whole thing out, you can check out the chapter 15 summary which will explain everything:
http://www.gradesaver.com/the-hound-of-the-baskervilles/study-guide/summary-chapter-xiv-xv