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