The great circle distance from LAT 35°57.2'N, LONG 05°45.7'W to LAT 24°25.3'N, LONG 83°02.6'W is 3966.5 miles and the initial course is 283.7°T. The latitude of the vertex is 38°09.4'N. What is the longitude of the vertex?

Correct Answer: Option A — 28°18.2'W

Great circle sailing formulas from Bowditch require Napier's rules of circular parts for right spherical triangles. Using the initial course and given positions, the vertex longitude is determined by applying the difference of longitude formula, yielding 28°18.2'W.