stuck on phycsi prlbem?

Question

1. The air temperature is 20 degree celcius. You are swimming underwater when when you hear a boat noise. Then, 3.5s later, you hear a crash. If the speed of sound in water is 1450 m/s, how long after the crash does your friend on the dock beside you hear the crash?

Answer 1

The speed of sound at that temperature is
331.3+sqrt(1+(273.15+20)/273.15)
=477.0 m/s

the crash is

1450*3.5=5075 m away.
The friend on the dock will hear the crash in
5075/477=10.6 seconds