2. (4 points) – suppose you are watching ten people leaving a bookstore. the clerk in the bookstore says that they sold a total of seven cookbooks and five unix network programming books to these ten customers. you are also told that two of the ten people didn’t buy anything and no one person purchased multiple copies of either text. you must show your work to receive full credit. a) how many people purchased at least one book? b) how many people purchased only the cookbook? c) how many people purchased both a cookbook and a network programming book?