You can measure the speed of sound the same way you measure the speed of a runner, with a stopwatch on a closed track.
At 21 degrees C (70°F), you should get 344 meters per second, or 1129 ft per second. At freezing, the numbers are 331 m/s or 1087 ft/s. The proper formula for the change in speed due to temperature is:
Where T is degrees Celsius. The works out to about a 0.1% change per degree Fahrenheit.
The Speed of sound in water is 1480 m/s or 4856 ft/s. More than 3000 miles per hour.
There is a project under way to take the earth's temperature by measuring the speed of sound between the USA and Australia.