Acar travels 50 miles in 2.5 hours. calculate the average velocity

In order to calculate velocity, we would need to know where the car was
when it started out, and where it was when it stopped.  Without any of this
information, the best we can do is calculate its average speed.

Average speed = (distance covered) / (time to cover the distance)

                           =     (50 miles)            /       (2.5 hours)

                           =              (50 / 2.5)      mile/hour

                           =                       20 mile/hour  .  

Sounds propagates through some kind of medium. usually it's air, but it goes just as well through solid objects like walls, windows etc. a soundwave will compress the (air)molecules in front of it, and if this increased density wave hits your ears, you register it as sound. solid objects like walls are a lot denser than air, this means that they will damp a wave, but also carry it easier.