Waves

A car P travelling at $20 \mathrm{~ms}^{-1}$ sounds its horn at a frequency of $400 \mathrm{~Hz}$. Another car $\mathrm{Q}$ is travelling behind the first car in the same direction with a velocity $40 \mathrm{~ms}^{-1}$. The frequency heard by the passenger of the car $\mathrm{Q}$ is approximately [Take, velocity of sound $=360 \mathrm{~ms}^{-1}$ ]