A man is going to northwards at $3km{h}^{-1},$ the wind appears to blow North-west. Actually it blows from the West. find the actual velocity of the wind $\left(inkm{h}^{-1}\right).$

Here , 

$$\begin{gathered} v_w=wind velocity , \\ {v}_m=velocity of man , \\ {v}_{wm} =velocity of wind with respect to man \end{gathered}$$

$\begin{array}{l}\therefore v_{wm}=v_w-v_m\\ \therefore \tan {45}^o\frac{v_m\sin {90}^o}{v_w-v_m\cos {90}^o}=\frac{v_m}{v_w}\\ \therefore v_w=v_m=3km{h}^{-1}\end{array}$