A butterfly is flying with a velocity. $4\sqrt{2}$ m/s in North-East direction. Wind is slowly blowing at 1m/s from North to South. The resultant displacement of the butterfly in 3 s is 

The given situation can be represented as 

In the above figure,  $v_1$ is the speed of wind and $v_{21}$  is the speed of butterfly with respect to wind 
So,  $v_{21}$ can be given as 
$$\begin{gathered} v_{21}=4\sqrt{2}\cos {45}^0\widehat{i}+4\sqrt{2}\sin {45}^0\widehat{j} \\ =4\sqrt{2}\times \frac{1}{\sqrt{2}}\widehat{i}+4\sqrt{2}\times \frac{1}{\sqrt{2}}\widehat{j}=4\widehat{i}+4\widehat{j} \end{gathered}$$

And $v_1$ can be given as $v_1=-\widehat{j}$   $\therefore$ velocity of butterfly can be given as 

$v_2=v_1+v_{21}=4\widehat{i}+4\widehat{j}-\widehat{j}=4\widehat{i}+3\widehat{j}$  $\therefore$  Displacement of butterfly,  $D=v_2\times t$

$=(4\widehat{i}+3\widehat{j})\times 3=12\widehat{i}+9\widehat{j}$   $\therefore$ magnitude of displacement, 

$\left|D\right|=\sqrt{{12}^2+9^2}=15m$