A source of sound S emitting waves of frequency 100 Hz and an observer O are located at some distance from each other. The source is moving with a speed of 19.4 ${ms}^{- 1}$ at an angle of 60° with the source observer line as shown in the figure.
The observer is at rest. The apparent frequency observed by the observer (velocity of sound in air 330 ${ms}^{- 1}$ ) is

Moderate