若已知数据x₁，x₂，x₃的平均数为a，那么数据2x₁+1，2x₂+1，2x₃+1的平均数为____ （用含a的代数式表示）．

阅读理解。

    Selena Gomez and I are scheduled to meet at a low­key coffee shop in Encino. Not wanting to keep the superstar waiting, I arrived at nine, 20 minutes early. As I was catching up on e­mails, Selena quietly scooted into the seat next to me. No bodyguard. Not even a drop of makeup. She was ten minutes early and no one else in the restaurant looked up so much. Selena was wearing Bebe shorts. She had a baby face and ordered a hot chocolate.

    After making small talk about what she wore for the shoot, she dived into the subject of her career. Selena declared 2012 the year of movies. She filmed three: Spring Breakers, a drama; The Getaway, an action flick; and Hotel Transylvania, a comedy. Each is a marked move away from the teen style that made her a household name.

    Now that her Disney days are behind her, Selena is at that unstable point in a child star's career where she is trying to grow up—both as a person(she turned 20 in July)and as an artist. “Being part of the Disney Channel was such a blessing, and I'm super happy with what my show accomplished, but acting is something I would like to take on more seriously.” She continued, “I don't necessarily feel accomplished. I want to create a whole different person when it comes to acting.”

    Selena has been working fulltime since she was seven years old and scored a role on Barney&Friends. In 2007, when she was offered the lead in Wizards of Waverly Place, Selena, her mother, and her stepfather uprooted from Texas to LA , where they are settling now.

Miss Gao is our teacher. We all like ____ (she).