Construct context-free grammars for the following language: {anbmc2n/n,m>= 0}

Prove that the following language is not context free.

Provide the rules for context-free grammars that generate the following languages. L4 = {w ∈ {a, b, c}  | |w| ≥ 3, |w| is odd, and the first symbol, middle symbol and last symbol of w are all different }