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 C — 28°18.2'W

Using Napier’s Rules for right spherical triangles, the vertex longitude is found by solving the spherical triangle formed by the pole, the vertex, and the departure point. Given the initial course and latitudes, the formula cos(Lon_v - Lon_1) = tan(Lat_1) / tan(Lat_v) confirms the vertex longitude is 28°18.2'W.