The Vikings came into Week 9 in desperation mode as they went against the 3-4 Cardinals, whom they lost the previous December in the desert. The Vikings came into the game wearing their purple pants and played the Cardinals in what was arguably a desperation game not only for the season, but head coach Brad Childress' job. His job had become more scrutinized after he acted alone to cut WR Randy Moss, which drew a bunch of boos and jeers at Childress. However, the action did not start until the 2nd quarter, when the Vikings drove down the field and had a 2nd and goal. Favre threw to Peterson behind the line, but Peterson dodged a few players and got into the end zone, which made the game 7-0 in the 2nd quarter. The very next play, when the Vikings kicked off, Stephens-Howling returned a kickoff 96 yards for a touchdown which tied the game. After that, the Vikings responded with kicker Ryan Longwell nailing a 21-yard field goal. They fell behind with QB Derek Anderson completing a 30-yard TD pass to WR Andre Roberts to close out the first half. This was followed by DB Michael Adams returning a Percy Harvin kickoff fumble 30 yards for a touchdown, and with kicker Jay Feely making a 22-yard field goal. The lead was closed down by Peterson as he got a 4-yard TD run, and by QB Brett Favre's 25-yard TD pass to TE Visanthe Shiancoe. In overtime the decision was made when Longwell successfully made a 35-yard field goal to give the Vikings the win, bringing their record up to 3-5 and temporarily saving their quarterback's and head coach's jobs.
Question: How many points were the Cardinals leading by at halftime?
Answer: 4