Robert takes the underground train to work and uses an escalator at the railway station. If Robert runs up 7 steps of the escalator, then it takes him 62.5 seconds to reach the top of the escalator. If he runs up 15 steps of the escalator, then it takes him only 42.5 seconds to reach the top. How many seconds would it take Robert to reach the top if he did not run up any steps of the escalator at all?   Hint Hint