1. The problem statement, all variables and given/known data A person, travelling eastward at a rate of 4.0 km/hr, observes that the wind seems to blow directly from the north; on doubling his speed the wind appears to come from the northeast; determine the direction of the wind and its velocity. 2. Relevant equations 3. The attempt at a solution My teacher has actually given us the answers on this question. However, I am stuck at the point where she says the Velocity of wind relative to person = Velocity of wind relative to the ground - velocity of person relative to the ground. I just can't understand this at all! Please help! Thank you in advance!