The Raiders began their 2011 campaign at Sports Authority Field at Mile High, for a Week 1 AFC West duel with the Denver Broncos in the second game of Monday Night Football's doubleheader.  Oakland trailed early in the first quarter as Broncos kicker Matt Prater got a 28-yard field goal.  The Raiders answered in the second quarter as quarterback Jason Campbell found fullback Marcel Reece on a 3-yard touchdown pass, followed by a 37-yard, a 21-yard, and an NFL record tying 63-yard field goal from kicker Sebastian Janikowski. Janikowski's leg helped put the Raiders up 16-3 at halftime. Denver answered in the third quarter as wide receiver Eric Decker returned a punt 90 yards for a touchdown, followed by Prater getting a 30-yard field goal. Oakland struck back in the fourth quarter with Campbell's 1-yard touchdown.  The Broncos tried to rally with quarterback Kyle Orton completing a 9-yard touchdown pass to running back Lance Ball, yet the Raiders' offense was able to run out the clock. With the win, not only did Oakland begin their season at 1-0, but they also snapped their 8-straight opening day losing streak.
Question: How many points were the Raiders leading by at the half?
Answer: 13