Please provide me with a correct solution to these problems. Thank you!

Give a context-free grammar for each of the following languages. You do not need to prove that your grammars are correct. However, if it is too difficult to verify the correctness of your grammars, you may lose points (even if they happen to be correct). You should therefore aim to give the simplest grammars possible, and it may be to your benefit to offer short explanations about how your grammars work. (a) L1={0n1mmn2m}. (b) L2={w{0,1}w=wR and the number of 1 's in w is divisible by 3}. (c) L3={akbncmk,n,m0 and k+n=m}. (d) L4={akbncmk,n,m0 and k+m=n}