Question

if you see the flash of a lighting bolt and 3 seconds later you hear the clap of thunder. how far away was the lighting bolt?

Answer 1

the speed of sound in air is approximately 340 m/s

the speed of light (from the flash) is approximately 3E8 m/s ... instantaneous for practical purposes

so the distance to the bolt is
... 3 s * 340 m/s