Help! I need to find out how to calculate the time difference... of:
118 degrees 15'W and
81 degrees 47'W

Please explain, I know you divide by 15 but?? :eek:

Are you trying to determine the difference in sunrise (or sunset) between the two longitudres? The earth rotates at 15 degrees per hour (that's because it turns a full 360 degrees in 24 hours), or 900 minutes/hour. Find the difference in longitude between the 2 points, and divide by 15 degrees/hour or 900 minutes/hour as needed.