Answer:
i believe the answer is a.
Explanation:
i say this because she starts off with 6 notebooks then her mom gives her n more meaning that part of the equation is 6+n. then it says she wants to use the same number of notebooks in each of her 3 classes, making that the denominator because you have to remember you have n, the unknown amount of notebooks.
good luck :)
i hope this helps
**please let me know if this was wrong**
have a nice day !!