BOTH INTERNATIONAL & INLAND You are heading due east (090°) and observe a vessel's red sidelight on your port beam. Which direction may the vessel be heading?

Correct Answer: Option C — southwest (225°)

A red sidelight is visible from dead ahead to 22.5 degrees abaft the beam on the port side. If you are heading 090 degrees and see a red light on your port beam, the other vessel must be heading in a direction that places her port side toward you, specifically 225 degrees.