How to find mean distance between galaxies from redshif?

[kdlsw]

If we know the mean number density of galaxies in the universe, the redshift z and the Hubble constant. Is it possible to find the mean distance between galaxies at such redshift?

The redshift gives a ratio of two distances between the same pair of bodies, at two different time due to the expansion of the universe. I don't understand how is this parameter related to the mean distance between galaxies. And how is it related to Hubble's law anyway?

The question is attached. All 3 parts are confusing me...Please show some approaching ideas or solution, thank you!

 

[Simon Bridge]

If you know the mean number density, what else do you need to know in order to work out the mean separation?