BOTH INTERNATIONAL & INLAND You see a red sidelight bearing NW (315°). That vessel may be heading in which direction?

Correct Answer: Option C — southwest (225°)

Rule 21 defines sidelights as showing an unbroken arc of 112.5 degrees. If you see a red (port) light bearing 315 degrees, the vessel is showing its port side to you. To present that aspect, the vessel must be heading in a direction that places your position to its starboard, specifically southwest (225 degrees).