4. If a machine has an efficiency of 80 %, and an ideal mechanical advantage of 10, what is its mechanical advantage?

The answer should be a.

Iisisisisososos9soslslsskosisosisi

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.