Answer in brief:

If it is 12 noon at 60°E longitude, then explain what would be the time at 30° W longitude?

Local time of any place is determined by its longitudinal location. The time at 30° W longitude can be determined with reference to know the time at any given longitudinal location.

the difference in the longitudinal stretch with known reference = 60°E - 30°W =90°

Time is taken to travel longitudinal degree = 4 minutes

Time taken for 90° = 90*4 = 360 minutes = 6 hours

Thus, if it is 12 noon at 60°E longitude, then time at 30° W longitude would be 6 AM.