Question 1101932
number of books bought AFTER=x
Cost of those books is 87.96-8=79.96
This is 4 extra books, because $79.96/4=$19.99
Note, the wording is not good.  The book club sends 8 books for $1 EACH.  That is needed to make this question answerable.  As written, it sounds like 8 books were for $1.