Mason and his friends were playing baseball outside his house when they saw lightning and heard thunder rumbling in the distance. They wanted to know how
far away the storm was, so they went inside, and as soon as they saw the next lightning flash, they started counting seconds until they heard the thunder. For every three seconds they counted, they knew the storm was about one kilometer away. Which of the following properties did Mason and his friends use to determine the distance of the storm?
1. speed of light
2. speed of sound
3. speed of the storm
4. speed of the lightning