Chemistry - Working out bond enthalpy - Guidance Needed!?

In a practise exam, I've been given this question:

" Given the following data:
C(s) + F2 (g) -> CF4 (g) ?H1 = -680 kJ Mol-1
F2(g) -> 2F(g) ?H2 = +158 kJ mol-1
C(s) -> C(g) ?H3 = +715 kJ mol-1

calculate the average bond enthalpy for the C-F bond".

My main confusion is over the first equation, which clearly isn't balanced?
I'm also unsure how I'm isolating the C-F bond. I think I should begin with reversing the CF4 equation, but the balance issue throws me off?

Can anyone guide me to getting the answer? (I don't have a mark scheme currently)

Thanks!
 
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