Consider the following prisoner's dilemma game. P2 P1 Cooperate Defect Cooperate Defect 60,60 0,75 75,0 30,30 a. Find the unique Nash equilibrium. b. Suppose the game is repeated for 10 periods. Find the subgame-perfect equilibrium of the 10- period finitely-repeated game. c. Suppose the game is repeated infinitely, and both players have a common discount factor B for future payoffs. How patient must the players be for cooperation to occur in equilibrium if both players use a grim trigger strategy? d. Again suppose the game is repeated infinitely, and both players have a common discount factor B for future payoffs. How patient must the players be for cooperation to occur in equilibrium if both players use a tit-for-tat strategy?