The Redskins' second regular season game, against the Philadelphia Eagles, started off with a Redskins field goal at the end of the first quarter. Less than five minutes into the second quarter, the Eagles scored a field goal to tie the game at 3-3. A few minutes later, the Eagles scored another field goal to take the lead 6-3, the only lead the Eagles would produce for the entirety of the game. Just before halftime, Jason Campbell hit Chris Cooley for a touchdown to end the first half up 10-6. In the third quarter, the Eagles and Redskins both scored another field goal, bringing the score to 13-9 prior to a Redskins drive that began with 1:15 remaining in the third quarter. That would eventually lead to Clinton Portis running for a six-yard touchdown early in the 4th quarter, bringing the score to 20-9. The Eagles, with a field goal late in the 4th quarter, were down by 8 as they drove down to the Redskins 9-yard line. The Eagles' drive stalled and they turned the ball over on downs with an incomplete pass. With possession on their own 9-yard line, the Redskins ran out the clock on their way to a victory. Final Score: 20-12.
Question: How many points were the Redskins leading by at the end of the first half?
Answer: 4