The Broncos played the Super Bowl XL champion Pittsburgh Steelers at Heinz Field in Pittsburgh, in a rematch of the 2005 AFC Championship Game.  The Broncos got on the scoreboard quick with Jake Plummer throwing a 16-yard touchdown strike to WR Rod Smith on their first drive of the game.  On the ensuing kickoff, the Steelers fumbled the ball, with the Broncos recovering deep into Steelers' territory.  Plummer then threw a 10-yard pass to WR Javon Walker to make the score 14-0. On the next drive, the Steelers got to the Denver 41-yard line when QB Ben Roethlisberger completed a 35-yard pass to WR Cedrick Wilson, who then fumbled the ball and the Broncos recovered. In the second quarter, the Steelers dominated play outscoring the Broncos 10-0 on the quarter.  Roethlisberger threw a 15-yard touchdown pass to RB Willie Parker for his first touchdown pass of the game.  The Steelers were about to score on their next possession when Roethlisberger threw an interception near the end zone to CB Champ Bailey.  After the Broncos showed no offense in the quarter, and the Steelers missed a 40-yard field goal, the quarter ended with the Steelers' Jeff Reed kicking a 46-yard field goal. In the third quarter, Denver quickly scored with a 72-yard end around run by Javon Walker.  On their next drive, the Steelers were driving down the field, when Roethlisberger threw another interception to Champ Bailey near the end zone. Denver was unable to get out of their own end zone after that and punted to the Steelers, who scored on the next drive with a 3-yard touchdown run by Willie Parker. Denver put the game to an end in the fourth quarter with another 10-yard touchdown pass from Plummer to Walker.  This came after the Steelers punted from their own 1-yard line and the Broncos began the series on the Steelers' 17-yard line.  Both the Steelers and the Broncos scored field goals on their next possessions, the Steelers with a 29-yard field goal and Denver with a 32-yard field goal. Pittsburgh again, down by 11, nearly made it a 4-point game when WR Hines Ward leaped into the end zone, but fumbled from a John Lynch (American football) tackle, whereby the Broncos safety Curome Cox recovered the fumble.  On the Steelers next possession, Roethlisberger again threw an interception, this time to Curome Cox, ending the game. With this win the Broncos remained tied with the Chargers in the AFC West with a 6-2 record.
Question: How many total yards did Willie Parker have on touchdown plays?
Answer: 18