The Xbox 360 launched with 14 games in North America and 13 in Europe. The console's best-selling game for 2005, Call of Duty 2, sold over a million copies. Five other games sold over a million copies in the console's first year on the market: Ghost Recon Advanced Warfighter, The Elder Scrolls IV: Oblivion, Dead or Alive 4, Saints Row, and Gears of War. Gears of War would become the best-selling game on the console with 3 million copies in 2006, before being surpassed in 2007 by Halo 3 with over 8 million copies.

Answer this question, if possible (if impossible, reply "unanswerable"): How many copies did Halo 3 sell?
8 million copies