The great circle distance from LAT 38°17'N, LONG 123°16'W to LAT 35°01'N, LONG 142°21'E is 4330 miles, and the initial course is 300.9°T. Determine the latitude of the vertex.

Correct Answer: Option B — 47°40.5'N

Great circle vertex latitude is determined using Napier's Rules of Circular Parts for right spherical triangles, solving via Bowditch formulas where the cosine of the vertex latitude equals the sine of the initial course multiplied by the cosine of the departure latitude.