you look up and see a helicopter pass directly overhead: 3.10 s later you hear the sound of the engines....?

Question

If the air temperature is 23.0 degrees celcius, how high was the helicopter flying?

Answer 1

speed of sound at 23 degrees celcius = 331.3 + 0.6 *23 = 345.6 m/s

height = 345.6*3.1 = 1071.36 m

Answer 2

343.1X3.1 = 1063.61 meters high ????

That was figured at 20 deg Celcius. The answer is probably not right, but it was the best I could do.
http://www.engineeringtoolbox.com/speed-sound-d_82.html