What started as a dominating performance ended with one of the most monumental collapses in franchise history as the Giants lost to the Tennessee Titans 24-21 after leading 21-0 with nine minutes remaining.  After stopping the Titans early in the first quarter, the Giants drove 52 yards in nine plays, mixing up the run and pass.  The drive culminated in a three-yard touchdown from Eli Manning to Plaxico Burress.  After a second Titans fumble, the Giants extended the margin with a 10-yard touchdown run by Brandon Jacobs.  The Giants opened up a 21-point lead when Jacobs scored again on a short run, late in the first half. The Giants continued to lead 21-0 until midway through the fourth quarter.  With the running game and short passing game moving the ball well, the Giants made the first of several mistakes.  Manning threw long to Burress and was intercepted.  After Vince Young was stopped on fourth down, the Giants committed a personal foul that kept the drive alive.  Young then threw a score to Bo Scaife bringing the Titans within 14.  After a Giants punt and big punt return from Adam "Pacman" Jones, Young struck again, this time on a one-yard bootleg.  New York was forced to punt again.  After the defense held on the first three plays, Young got away on a fluke after Giants' pass rusher Mathias Kiwanuka, thinking the play was dead, unbelievably let go of Vince Young on a sack-to-be, leading to a first down.  Six plays later, the Titans were back in the end zone when Brandon Jones caught a Young pass to tie the game with less than a minute remaining. Although the game appeared to be headed to overtime, Manning attempted to lead a furious drive into field goal range. Instead, he threw an ill-advised sideline pass, which was intercepted at the 50-yard line.  Two passes from Young was enough to set up a 49-yard field goal, which kicker Rob Bironas connected on as time expired, giving the Titans the improbable victory.  Manning finished 18 for 28 for 143 yards, a touchdown and two interceptions.  Tiki Barber had 85 yards rushing and Jeremy Shockey had five catches in the devastating defeat.
Question: How many points did the Titans need for a comeback?
Answer: 21