You are underway on a course of 135°pgc at 15 knots, and you sight a lighthouse dead ahead at a range of 12.5 miles at 1145. What course would you steer to leave the lighthouse 3.0 miles off your port beam?

Correct Answer: Option B — 149°pgc

The light is dead ahead at 12.5 miles. To pass 3 miles off, the required course change is arcsin(3 / 12.5) = 13.9 degrees. Applying this shift to the 135-degree pgc course, moving away from the light to the port side, results in a new course of 149 degrees pgc.