Passage: During the 1970s, Led Zeppelin reached new heights of commercial and critical success that made them one of the most influential groups of the era, eclipsing their earlier achievements. The band's image also changed as the members began to wear elaborate, flamboyant clothing, with Page taking the lead on the flamboyant appearance by wearing a glittering moon-and-stars outfit. Led Zeppelin changed their show by using things such as lasers, professional light shows and mirror balls. They began travelling in a private jet airliner, a Boeing 720 (nicknamed the Starship), rented out entire sections of hotels (including the Continental Hyatt House in Los Angeles, known colloquially as the "Riot House"), and became the subject of frequently repeated stories of debauchery. One involved John Bonham riding a motorcycle through a rented floor of the Riot House, while another involved the destruction of a room in the Tokyo Hilton, leading to the group being banned from that establishment for life. Although Led Zeppelin developed a reputation for trashing their hotel suites and throwing television sets out of the windows, some suggest that these tales have been exaggerated. According to music journalist Chris Welch, "[Led Zeppelin's] travels spawned many stories, but it was a myth that [they] were constantly engaged in acts of wanton destruction and lewd behaviour".Led Zeppelin released their fourth album on 8 November 1971. In response to the treatment they had received from critics, particularly after Led Zeppelin III, the band decided to release the fourth album with no title, though it is variously referred to as Led Zeppelin IV, Untitled, IV, or, due to the four symbols appearing on the record label, as Four Symbols, Zoso or Runes. In addition to lacking a title, the original cover featured no band name, as the group wished to be anonymous and to avoid easy pigeonholing by the press. With 37 million copies sold, Led Zeppelin IV is one of the best-selling albums in history, and its massive popularity cemented Led...

Question: How many copies did Led Zeppelin IV sell in 2006?
23 million