What is the time at 75° west longitude if it is 10:00 a.m. in Greenwich, England?

To determine the local time at 75° west longitude when it is 10:00 a.m. in Greenwich, England (which is at 0° longitude), it is important to understand how time zones are calculated based on longitude. The Earth is divided into 24 time zones, each generally covering 15 degrees of longitude. This means that for every 15 degrees of longitude, the local time changes by one hour.

Since 75° west is located to the west of Greenwich, we need to calculate the time difference. Specifically, for every 15 degrees west, the local time is one hour earlier than in Greenwich. Thus, to find the time at 75° west, we can divide 75 by 15:

75° ÷ 15° = 5 hours

This indicates that the local time at 75° west is 5 hours earlier than the time in Greenwich. Therefore, if it is 10:00 a.m. in Greenwich, we subtract 5 hours:

10:00 a.m. - 5 hours = 5:00 a.m.

This result, 5:00 a.m., aligns perfectly with the correct answer. The time at 75° west longitude is indeed 5