For this case we have the following equation:
![P = -Q + 42](https://img.qammunity.org/2020/formulas/mathematics/middle-school/lrvbvq3nu2s21j5k482dvtspeqgjldx4pr.png)
Where:
P: Represents the price of magazines
Q: Represents the quantity of magazines sold
If the bookstore charges 5 for a magazine, then we substitute
![P = 5](https://img.qammunity.org/2020/formulas/mathematics/middle-school/77qahfyyulaymes8w9orqxw31ouwn5t4gq.png)
![5 = -Q + 42\\Q = 42-5\\Q = 37](https://img.qammunity.org/2020/formulas/mathematics/middle-school/cot0guowmuj8wws97me56j0f2mpk40ibwi.png)
Thus, the bookstore can expect to sell 37 magazines.
Answer:
37 magazines