Correct Answer - A::D
Let the speed of the car =xm/sec
So, frequency heard at car n
`v=(v+v_(car))/vxxn_0=(324+x)/324xx400`
and frequency heard by operator for reflected sound wave
`n_1=324/(324-x)xxn`
`rarr 410=324/(324-x)xx(324+x)/324xx400`
`rarr 324(410-400)=810xrarrx=4m/sec`