Identify the problem that represents the join, result unknown structure.
◦ Maryann had 3 library books before she checked out 2 more. How many did she have all together?
◦ Maryann had 5 library books before she returned 2 of them. How many does she have now?
◦ Maryann had 4 nonfiction books and 2 fiction. How many more nonfiction books does she have?
◦ Maryann had 9 library books and Jim had 4. How many more did Maryann have than Jim?