In terms of the structure and boiling point of graphite, explain why the melting point is high

Each carbon atom in graphite is bonded to three other carbon atoms. These carbon atoms are linked by covalent bonds - which are very strong. Graphite is arranged in sheet like structures and between each layer there are Van der Waals intermolecular forces which are weak in comparison to the covalent bonds. For each carbon atom there is a delocalised electron - due to it only forming three bonds. 

These delocalised electrons will be shared by all the atoms on a single layer of graphite, increasing the strength of the bond between atoms, this also increases the stability of the structure, thus making the melting point high as this bonds are more difficult to break as more energy will be required to break them.