The Texans began their 2008 campaign on the road against the Pittsburgh Steelers.  In the first quarter, Houston trailed early as Steelers RB Willie Parker got a 7-yard TD run.  In the second quarter, the Texans continued to trail as Parker got a 13-yard TD run, while QB Ben Roethlisberger completed a 13-yard TD pass to WR Hines Ward.  Houston would end the half with kicker Kris Brown getting a 34-yard field goal.  In the third quarter, the Texans continued to trail as Parker got a 4-yard TD run, while Roethlisberger and Ward hooked up with each other again on a 16-yard TD pass.  In the fourth quarter, Houston replied with QB Matt Schaub completing a 14-yard TD pass to WR Kevin Walter.  Pittsburgh would respond with kicker Jeff Reed nailing a 44-yard field goal.  The Texans would close out the game with Schaub getting a 4-yard TD run.
Question: How many yards longer was Willie Parker's second touchdown run compared to his first?
Answer: 6