Two tuning forks $A$  and $B$  having a frequency of 500 Hz each are placed with $B$ to the right of  $A$  An obsever in between the forks is moving towards  $B$ with a speed of 25 m/s.  The speed of sound is 345 m/s and the wind speed is 5 m/s from  $A$ to  $B$.  Calculate the difference in the two frequencies heard by observer. (Hz)

Let the fork at  $A$ be source $S_1$  and the fork at  $B$ source $S_2.$   For the sound from  $S_1:$
Apparent frequency  $=f_1=f\left(\frac{v-V_0}{v-V_s}\right)$
Here $v=345+5=350$  m/s as wind and sound are in same directions.
$V_0=+25$ m/s, $V_s=0$  m/s
$\Rightarrow f_1=500\left(\frac{350-25}{350-0}\right)=464.3$ Hz
For the sound from source $S_2:v=345-5=340$  m/s as wind is in opposite direction to that of sound.
$V_s=0$ m/s, $V_0=-25$  m/s
$\Rightarrow f_2=f\left(\frac{v-V_0}{v-V_s}\right)=500\left(\frac{v-(-25)}{v-0}\right)=\frac{500\times 365}{340}$
$=536.80$ Hz
$\Rightarrow f_2-f_1=(536.80-464.30)=72.5Hz$