Suppose that the advertising arms race in Example 23.2 is repeated a second time by the same

Question:

Suppose that the advertising arms race in Example 23.2 is repeated a second time by the same two firms.
(a) Draw an extensive form for the two-period game, showing all strategies for both firms in both periods.
(b) Solve for all the pure-strategy NE of the game.
(c) Solve for the unique SPNE of the game.