Read this and answer the question. If the question is unanswerable, say "unanswerable".

In league competitions, games may end in a draw. In knockout competitions where a winner is required various methods may be employed to break such a deadlock, some competitions may invoke replays. A game tied at the end of regulation time may go into extra time, which consists of two further 15-minute periods. If the score is still tied after extra time, some competitions allow the use of penalty shootouts (known officially in the Laws of the Game as "kicks from the penalty mark") to determine which team will progress to the next stage of the tournament. Goals scored during extra time periods count toward the final score of the game, but kicks from the penalty mark are only used to decide the team that progresses to the next part of the tournament (with goals scored in a penalty shootout not making up part of the final score).

Extra time has two periods which each are how long in minutes?
15