Billie B Brown Mystery collection (6 books), by Sally Rippin. NWOT.

For children who loved the characters in Billie B. Brown and Hey Jack! and are ready for a higher reading level there is the Billie B. Mysteries series. In these books a slightly older Billie, her best friend, Jack, and other familiar friends from the original series, solve mysteries at school and in the neighborhood, using their smarts and common sense to get to the bottom of things. The Billie B. Mystery series features a strong, smart girl protagonist; engaging, real-life mysteries; and, demonstrates reasoning and problem-solving skills while showcasing teamwork and cooperation. Early readers will enjoy the larger font and illustrations throughout the series, designed with them in mind. This collection includes the following titles: Code Breakers, Playground Detectives, Spooky House, Strawberry Thief, Stolen Stash, and Treasure Hunt.