5x-4=7x-24
If x= 10, there are 5x 10-4=46 books.
In fact, this is profit and loss problem, who came into contact with elementary school 3. There is a special formula to answer, and the landlord is interested in Baidu "profit and loss problem".
In 2007, the choice of fill-in-the-blank questions in Mathematics II was changed to 16 questions. Since