Context free grammar for $\{ a^i b^n a^n \mid i \ge 0, n \ge 0 \}$
You could break down the language into simpler parts, e.g., you can generate languages separately for $a^i$ and $b^na^n$, then concatenate them in the end (we know that CFG's are closed under concatenation). 

In your case, you can do


  A $\rightarrow$ aA | $\epsilon$


to generate $a^i$, and


  B $\rightarrow$ bBa | $\epsilon$


to generate $b^na^n$, then concatenate by doing:


  S $\rightarrow$ AB