A car travels with a speed of 40   km   h - 1 . Rain drops are falling at a constant speed…

Here the car moves with speed $v_{CE}=40 \mathrm{km} {\mathrm{h}}^{-1}$ and raindrops are falling at a constant speed vertically with respect to the Earth as shown in the figure below.

 

Now, velocity of car relative to the rain is calculated using the relation, $v_{RC}=\frac{v_{CE}}{\sin \theta }=\frac{40}{\sin 30°}=\frac{40}{0.5}=80 \mathrm{km} {\mathrm{h}}^{-1}$.