Calculus question please help?

Suppose that when a busy restaurant charges $7 for its tomato appetizer, an average of 60 people order the dish each night. When it drops the price of the appetizer to $5, the number ordering it rises to 66. ume that the demand q is a linear function of the price p. If each appetizer costs the restaurant $3 to make, use calculus to find the price it should charge to maximize its profit from the appetizer.