In week 4, the Lions hosted their NFC North Division rivals the Minnesota Vikings. The Vikings took an early lead when Percy Harvin returned the opening kickoff 105 yards for a touchdown. The Lions responded with a 40-yard field goal by Jason Hanson. Minnesota's Blair Walsh then kicked a field goal from 49 yards out. Both teams kicked a field goal in the second quarter, first Minnesota's Blair Walsh from 27 yards out, then Detroit's Jason Hanson from 31 yards. The only scoring drive of the third quarter was when the Vikings' Marcus Sherels returned a punt 77 yards for a touchdown. The Lions scored the only points of the final quarter when quarterback Matthew Stafford completed a 1-yard run for a touchdown.  With the loss, the Lions went into their bye week at 1-3.

Based on the above article, answer a question. How many field goals were scored during the first half?
4