Calculating average bond enthalpy question?

Given the following data:
1. C(s) + F2(g) -> CF4(g): [delta]H = -680kJ/mol
2. F2(g) -> 2F(g): [delta]H = +158kJ/mol
3. C(s) -> C(g): [delta]H = +715kJ/mol

Calculate the average enthalpy (in kJ/mol) for the C-F bond.

Thanks
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