Answers for textbook chapters are usually available in an answer key provided by the textbook's publisher, which can be in a book and/or online format. If it is in book format, the answer key is either within the textbook itself (usually at the end) or published as an accompanying volume.
Some educational institutions provide access to online answer keys through their websites, as the University of Kentucky does with "The Art of Writing Reasonable Organic Reaction Mechanisms." Seton Educational Media provides many of its answer keys inside its textbooks. An example of an answer key published as a separate book or booklet is "A Teaching Textbook's Algebra 1."