I am utterly confused with this problem, I am not quite sure how to formulate an equation to solve for the answer : The speed of sound in steel is about 4.2 kilometers per second. A steel rail is struck with a hammer, and there is an observer some distance away with one ear to the rail. The observer measures 1.60 seconds between hearing the sound through the rail and hearing the sound through the air. If the air temperature is 20 degrees Celsius and there is no wind, how far away is the observer? Just looking for someone to show me where to begin any help appreciated?