Original author here. Someone else discovered this and notified me about three weeks ago. Amazon has a site for reporting infringement, so I submitted my claim of ownership. I received an immediate automated response promising a follow up, but I have yet to hear anything more.

In the book's front matter I grant permission for anyone to use the book freely and to make as many copies as they like as long as the original copyright notice remains intact. It started out as my small way of helping my students who are facing escalating higher education costs. Over the years, I've received feedback from other instructors at both the university and high school level who appreciate having this option available for their students.