2. (25 %) An urn contents 10 balls, numbered from 1 to 10. For each game, the player will select 2 balls and will win the game, if the sum of the numbers on the balls is 10. Let $X$ be the number of games that the player needs to play for 1st win.

(a) Find the p.m.f. of \( X \) and \( \operatorname{E}(X) \) if the 2 balls are selected with replacement.