The iris dilates and constricts thus, regulating

Function. The iris is a contractile structure, consisting mainly of smooth muscle, surrounding the pupil. Light enters the eye through the pupil, and the iris regulates the amount of light by controlling the size of the pupil. When the sphincter pupillae contract, the iris decreases or constricts the size of the pupil. Hope this is what your looking for. :)

answer; i do believe the correct answer is (25) times faster;

well say a good goal is to do 150 sit ups in a week! or 90 pull ups a day. even 60 push ups in a month these are all fair goals!