Rain drops fall vertically at a speed of $20 \mathrm{m }{\mathrm{s}}^{-1}$. At what angle (in degree) do they fall on the wind screen of a car moving with a velocity $15 \mathrm{m }{\mathrm{s}}^{-1}$, if the wind screen is inclined at an angle of $23°$ to the vertical? [${\tan }^{-1}\left(0.75\right)\approx 37°$]