USE WORKSHEET: A commuter train blows its $200-$Hz horn as it approaches a crossing. The speed of sound is $331$ m$/$s$.($a$)$ An observer waiting at the crossing receives a frequency of $211$ Hz$.$ What is the speed of the train in m$/$s$?$

USE WORKSHEET: A commuter train blows its $200-$Hz horn as it approaches a crossing. The speed of sound is $331$ m$/$s$.($a$)$ An observer waiting at the crossing receives a frequency of $211$ Hz$.$ What is the speed of the train in m$/$s$?$