This is a pretty interesting question. I've heard from my student that none of his classmates could solve it. Even some of his teachers had problems with it. It did make me think for a while, but once you have the correct diagram, it should not be too difficult.
Suppose a plane flies North at 100 km/h. The wind seems to be blowing at a bearing of 030(degrees). If the plane reduces its speed to 50 km/h, the wind seems to be blowing at a bearing of 050. What is the actual speed of the wind?