You drive an old car on a straight, level highway at \(45 \mathrm{mi} / \mathrm{h}\) for \(10 \mathrm{mi}\), and then the car stalls. You leave the car and, continuing in the direction in which you were driving, walk to a friend's house \(2.0 \mathrm{mi}\) away, arriving \(40 \mathrm{~min}\) after you begin walking. What is your average speed during the whole trip?