The frequency of echo will be _______ \( \text{Hz} \) if the train blowing a whistle of frequency \( 320 \, \text{Hz} \) is moving with a velocity of \( 36 \, \text{km/h} \) towards a hill from which an echo is heard by the train driver. Velocity of sound in air is \( 330 \, \text{m/s} \).
