Please help with a hard chem problem?

Question

I tried doing this problem but I guess I don't understand the concept.
Using the starting chemicals F, F2, CH4 or CH3 make up a free radical.

Initiation step:
propagation step:
Termination step;
You can use two of the radicals given then go through the steps. And please explain. Thanks for helping!

Answer 1

Initiation

CH4 + F -> CH3. + HF

Propagation

CH3. + F2 -> CH3F + F.

Termination

F. + F. -> F2

CH3. + CH3. -> C2H6.