Answer
given,
speed of sound = 344 m/s
speed of train = 30 m/s
frequency emitted by the train = 262 Hz
Doppler's effect
f_L is the frequency of listener
f_S is the frequency of the source of the sound
v is the speed of the sound
v_L is the speed of listener.
v_S is the speed of the source
a) Speed of the passenger in another train , v = 18 m/s
another train is moving in opposite direction and approaching
v_L is positive as the listener is moving forward.
v_S is negative at the source is moving toward the listener.
b) Speed of the passenger in another train , v = 18 m/s
another train is moving in opposite direction and receding
v_L is negative as the listener is moving away from source.
v_S is positive at the source is moving away the listener.