two trains emit 516 Hz whistles. One train is stationary. The conductor on the stationary train hears a 3.5 Hz beat frequency when the other train

two trains emit 516 Hz whistles. One train is stationary. The conductor on the stationary train hears a 3.5 Hz beat frequency when the other train approaches. What is the speed of the moving train?
Δf = (v/s) * f0s is speed of speed in airv is speed of trainf0 is frequency of sirenf0 = 516 Hzs = 340.29 m/sΔf = 3.5 Hzv = (3.5 / 516) * 340.29= 2.31 m/s