How to do (a) and (b)?

4. Consider a game in which Player I chooses rows, Player 2 chooses columns and Player 3 chooses matrices. Only Player 3's payoffs are given below. A B C D L R L R L. R L R 7 9 0 T 0 0 0 6 0 6 B 0 B 0 B 0 9 B (a) Show that D is not a best response for Player 3 against any combination of (mixed) strategies of Players I and 2. (18 marks) (b) Prove that D is not dominated by any (mixed) strategies of Player 3. (15 marks)