On the morning of 11 September 2001, 19 men affiliated with al-Qaeda hijacked four airliners all bound for California. Once the hijackers assumed control of the airliners, they told the passengers that they had the bomb on board and would spare the lives of passengers and crew once their demands were met – no passenger and crew actually suspected that they would use the airliners as suicide weapons since it had never happened before in history. The hijackers – members of al-Qaeda's Hamburg cell – intentionally crashed two airliners into the Twin Towers of the World Trade Center in New York City. Both buildings collapsed within two hours from fire damage related to the crashes, destroying nearby buildings and damaging others. The hijackers crashed a third airliner into the Pentagon in Arlington County, Virginia, just outside Washington D.C. The fourth plane crashed into a field near Shanksville, Pennsylvania, after some of its passengers and flight crew attempted to retake control of the plane, which the hijackers had redirected toward Washington D.C., to target the White House, or the U.S. Capitol. No flights had survivors. A total of 2,977 victims and the 19 hijackers perished in the attacks.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): How long did it take for the Pentagon to collapse?
unanswerable