I see that there are 20 interstitial site locations for an hcp crystal. Please show all the coordinates (x, y, z) of those locations in terms of the lattice constant ("a") unit. Justify your coordinate location values (that is, show how you obtained those x, y, z values).
Note: If you don't know the answer fully, but still answer partially, you will get a downvote as you will destroy someone else's possibility to answer correctly here.
To see those locations, you can type in the Google search bar: "msestudent hexagonal close packed hcp unit cell". Then click on the first link, and you will see this image from there (the lower right one shows all interstitial locations - we need their coordinates now):
Octahedral Sites
Tetrahedral Sites
An interstitial site among neighboring host atoms
An interstitial site among neighboring host atoms
Octahedral and Tetrahedral Interstitials in HCP
All interstitial site positions within HCP unit cell