Ben is running a race in half a year. To prepare, he creates a training schedule in which the distance of his longest run every week increase by a constant amount. If Ben's training schedule requires that his longest run in week 8 is a distance of 14 miles and his longest run in week 20 is a distance of 30 miles, which of the following best describes how the distance Ben runs changes between week 8 and week 20 of his training schedule?