Final answer:
The time in city 'B' at 60°E longitude would be 4pm if it is 6am in city 'A' at 90°W longitude.
Step-by-step explanation:
The time difference between two locations can be determined by calculating the difference in longitude. One degree of longitude corresponds to a time difference of 4 minutes. In this case, city 'A' is at 90°W and city 'B' is at 60°E. The difference in longitude is 150°, which corresponds to a time difference of 10 hours (150° × 4 minutes).
If it is 6am in city 'A', then it would be 4pm in city 'B' (6am + 10 hours) since city 'B' is 10 hours ahead of city 'A'.