Write a question about the following article: Coming off their home win over the Bengals, the Seahawks flew to Monster Park for an NFC West duel with the San Francisco 49ers.  After a scoreless first quarter, the 'Hawks took flight in the second quarter with kicker Josh Brown getting a 23-yard field goal, along with QB Matt Hasselbeck completing a 17-yard TD pass to WR Bobby Engram.  Seattle ended the half with Brown kicking a 31-yard field goal. In the third quarter, the Seahawks went back to work with Hasselbeck completing a 14-yard TD pass to TE Marcus Pollard.  The 49ers got their only score of the game with kicker Joe Nedney getting a 43-yard field goal.  In the fourth quarter, Seattle wrapped up the game with Brown nailing a 25-yard field goal. With their first divisional win in five games, the Seahawks improved to 3-1.  Fullback Mack Strong played in his 200th game as a Seahawk, becoming only the second player to do so.
how many yards did brown kick at the half?