Speed of moving car that hears a whistle

A stationary whistle emits a sound of 188 Hz. If a car hears the whistle with a frequency of 194 Hz, how fast was it moving (in m/s)? Use 340 m/s for the sound velocity.

For a sationary source like this question:

f ' (detected) = f(original) ( v (sound) + v (detector)) / v (sound)

.'. v = 194/188 * 340 - 340 = 10.85 m/s