Maths Question - Tks for helping?

Matt, who is often late for appointments, walks up a moving escalator in the train station one step at a time. When he moves quickly at the rate of 2 steps per second, he reaches the top after taking 24 steps. When he is tired, he climbs at the rate of 1 step per second & reaches the top after taking 15 steps. How long would Matt take to reach the top if, on a rare day, he just stood on the escalator?