The firms simultaneously set prices at regular intervals. In the equilibrium of this game (if played only once), each firm selects the low price. However, the firms are playing this game repeatedly, for an infinite period of time. The firms utilize trigger strategies in order to maintain the collusive outcome. Suppose that both firms adopt the grim trigger atrategy. They continue charging the high price unless one of them cheats. Upon one of them charging the low pice, they play the equilibrium, low-price strategy for the rest of the game. What has to be true about the interest rate (r) for cooperation to be sustainable? r25%r50%