There are four basket-ball players A, B, C, D. Initially, the ball iswith A. The ball is always passed from one person to a different person. In how many ways can the ball come back to A after sevenpasses? (For example A → C → B → D → A → B → C → A andA → D → A → D → C → A → B → A are two ways in which the ballcan come back to A after seven passes.)