Can someone answer this:

What the Russell Paradox is (a complete proof that at some point you will want to prove that certain assumption leads to a contradictiion). And then Explain why it is so bad that a contradiction can be proved somewhere.( why ncant we just ignore the fact that in some remote corner of set theory this contradiction arises?), And Finally my 3rd question abotu russel paradox iii) Assuming a Statement B, which happens tobe a contradiction, prove that 6=21.