The correct answer is option 4: sunset at London will be 6 hours earlier than at St. Louis.

To understand why this is the correct answer, we need to understand how time zones work. Time zones are based on the Earth`s rotation. As the Earth rotates, different parts of the world experience daylight and darkness at different times.

The Earth is divided into 24 time zones, each approximately 15 degrees of longitude apart. This means that for every 15 degree change in longitude, there is a one-hour difference in time.

In the question, it states that London and St. Louis are 90 degrees of longitude apart. Therefore, there is a 6-hour time difference between the two cities.

Since the question specifically asks about the time of sunset, we can deduce that the correct answer is option 4. Since St. Louis is west of London, it will experience sunset 6 hours later than London. Therefore, sunset at London will be 6 hours earlier than at St. Louis.

Alert - correct answer should be option 3: sunset at London will be 6 hours later than at St. Louis. Since St. Louis is west of London, it will experience sunset 6 hours earlier than London, not