Fat Tiger and Nobita agreed to exchange Christmas gifts, but they forgot to agree on the price range of the gifts. Both parties have two choices: "buy expensive gifts" or "buy cheap gifts". Only after both parties send gifts at the same time, will they know which gift the other has given. The benefits to gift results If both parties give each other expensive gifts, the benefits for both are 7; if both parties give each other Suppose that Fat Tiger gave noble gifts and Nobita gave cheap gifts. At this time, Fat Tiger is angry and If Nobita gave noble gifts and Fat Tiger gave cheap gifts. Fat Tiger felt that he had earned it and gained benefits. (a) Is there a Nash equilibrium? If so, what is the strategy of the two and what are (b) If Nobita first gave gifts on Christmas Eve, and Fat Tiger returned the gifts on Christmas Day, please find the balance through backwacd induction, and please write down their respective strategies and benefits when the balance is reached