Exercise 30

A ship is sailing with speed and direction $\vec{v}_{1}$; the wind blows apparently (judging by the vane on the mast) in the direction of a vector $\vec{a}$; on changing the direction and speed of the ship from $\vec{v}_{1}$ to $\vec{v}_{2}$ the apparent wind is in the direction of a vector $\vec{b}$.

Find the vector velocity of the wind.