Puzzle - Cannibals and the hat puzzle 1 - Answer

C will give the answer as black.

If B and C were wearing white hats then A would have been able to give correct answer.
Since, A does not know the answer, B & C are either both wearing black hats or one black and one white hat.

If C was wearing a white hat, then B could have been sure that he would be wearing a black hat.
Since B was not able to find the correct answer, it means C is wearing a black hat.