Please solve

The buyer for a retail store located in a shopping mall has convinced himself that if he prices small personal fans at $x apiece, the weekly profit made by the store on sale of the fans will be given by the profit function P(a) = - x2 + 40x - 220. a. If the store is currently selling the small personal fans for $10, what is the average rate of change in the weekly profit if it increases the selling price of each fan to $11. CA per week b. If the store is currently selling the small personal fans for $20, what is the average rate of change in the weekly profit if it increases the selling price of each fan to $21. per week