The great circle distance from LAT 35°08.0'S, LONG 19°26.0'E to LAT 33°16.0'S, LONG 115°36.0'E is 4559 miles and the initial course is 121°T. Determine the longitude of the vertex.

Correct Answer: Option B — 65°45.9'E

Applying Bowditch's great circle sailing equations, the longitude of the vertex is derived by combining the departure position's longitude with the calculated difference in longitude, determined via the initial course angle and departure latitude.