any help greatly appreciated

For this case we have the following equation:
[tex]P = -Q + 42[/tex]
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 [tex]P = 5[/tex]
[tex]5 = -Q + 42\\Q = 42-5\\Q = 37[/tex]
Thus, the bookstore can expect to sell 37 magazines.
Answer:
37 magazines