Fermi energy (in graphite)

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Homework Statement

Graphite has a structure of parallel planes weakly interacting with each others such that for many effects it can be considered as two dimensional. Each plane has a hexagonal (honeycomb) structure with a single C atom by site which gives 1 electron of conduction. Assume that the model of free electrons can be applied to all conduction electrons, find the Fermi energy.

Homework Equations

Not really sure. Are there some missing data?

The Attempt at a Solution

What boggles me is that there's no volume given nor electron density. I don't think I can calculate the latter either, because even though I know there is 1 atom per elementary unit, I do not know the distance between atoms (not sure it even makes sense in a honeycomb structure). Thus I don't really know how to tackle the problem.
I know that $E_F= \frac{\hbar ^2 \pi n }{m}$. I know that n is the density of electron for an area unit but that number is an unknown in the problem.
I'd like some tip to start the problem, thank you!

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