Please help me with the answer for 19 th question please

First find the Velocity in the direction of Observer from Source
Which is vcos∅ = 20m/s × 1/2 {cos∅=Base/Hypotenuse}
... v = 10m/s
Now apply formula of Doppler's effect
μ'=μ×v/(v-v°)
μ'=640×330/330-10
μ'=640×330/320
μ'=660 Hz
Where μ'→Final Frequency and μ→Initial frequency

 

In the above figure s is the position of locomotive and O is the position of observer when the locomotive whistle.
Angle SAO = 90 
AO = 0.6 mile
SA = 1 mile 
Component of Vs along SO 
V' = Vs CosQ 
CosQ = SA/SO 
= 0.857 
Speed of locomotive = 80 mile/hour = 0.22mile/sec 
Therefor 
V' = 0.22 * 0.857 = 0.019 mile/sec 
The apparent frequency when source is in motion 
f = 0.20/(0.20-0.019) *400 = 442 Hz