Completing the Square for Quadratics

Hannah is selling homemade hats. So far, she has been selling the hats at $\$10$ per hat and typically sells $100$ hats a week. $\\$ Hannah is a smart entrepreneur and she knows that if she increases the price, less people will buy her hats. She finds that for every $\$1$ she raises the price, $5$ fewer hats will be bought. $\\$ Create a profit function for this scenario and find which price she should sell her hats for in order to maximize the profit.