A ship is in longitude 54°00'W on a true course of 270°. The ship's clocks are on the proper time zone. At what longitude should the clocks be changed to maintain the proper zone time?

Correct Answer: Option D — 67°30'W

In USCG General Navigation principles (Bowditch, Light Lists, and Coast Pilots), regarding 'A ship is in longitude 54°00'W on a true course of 270°. The ship's clocks are on the proper time zone. At what longitude should the clocks be changed to maintain the proper zone time', the verified fact is: '67°30'W'.