I have to design an experiment to measure the speed of sound.

We're given a tape measure and a stopwatch. The temperature of the air will be measured too.

So I know you're probably not going to tell me (one of the ways) how to do it, but do you have any hints?

The only thing I can think of is:
Two people stand far apart from each other, and the distance is measured. One person makes a loud noise, and the other person records the time it took for the sound to reach them with a stopwatch. (But that's going to be...so difficult to do...)

Thanks,
Lucy