Christine and Pamela, both teachers, are adding books to their class libraries. Christine's classroom started out with a collection of only 2 books, but she plans to purchase an additional 2 books per week. Pamela's library started out with 5 books, and she has enough money in her budget to purchase another 1 book per week. At some point, the two teachers' libraries will contain the same number of books. How many weeks will that take?