Formula to find sunrise/sunset time difference

[apolutrosi]

Homework Statement

In a physical Science class we were mistakenly given the wrong homework question. The question " Relative to the Sun. Earth turns 15° in longitude per hour of time, At the latitude of most of the United States , this coresponds to a distance of about 1200 km. If there is a town A, 240 km west of town B, and both towns are at the same latitude, approximately how much earlier or later does the sun rise at town A than town B ?


I do no remember how I came up with this answer nor do I know how to even start approaching it. As I said we were given this question by mistake and so we have not covered a solution in class. I did have the right answer of approx 9.12 minutes but I do not remember how I arrived at this answer. Can anybody share with me a formula I can use to come to the correct answer to this question.

Thank you

 

[Borek]

This is simple proportion. If the distance is 1200 km, Sun will rise exactly 1 hour earlier. If there is 600 km, Sun will rise half an hour earlier. And so on.

BTW: 9.12 doesn't look like a correct answer.