Velocity of sound \(=330 \,m / s\)

Frequency of incident sound on wall \(\left(f_1\right)=\frac{v}{v-v_s} \times f\)

Frequency of sound observed by driver \(\left(f_2\right)=\frac{v+v_s}{v} \times f_1\)

or \(f_2=\frac{v+v_s}{v-v_s} \times 600\)

or \(f_2=\frac{360}{300} \times 600\)

or \(f_2=720 \,Hz\)