The longitude of the upper vertex of a great circle track is 169°E. What is the longitude of the lower vertex?

Correct Answer: Option A — 011°W

Upper and lower vertices of a great circle are diametrically opposed, separated by exactly 180° of longitude. Subtracting the upper vertex longitude of 169°E from 180° yields 11°, changing the hemisphere to West (011°W), according to Bowditch spherical navigation principles.