The Pittsburgh Steelers headed to Oakland, CA in week three to take on their long-time rivals.  The Steelers would score first on a 4-yard touchdown pass from Ben Roethlisberger to tight end Heath Miller, but the Raiders would respond when running back Darren McFadden would break loose on a run and take it 64-yards for a touchdown.  Heath Miller would catch another 4-yard touchdown pass, and the Raiders would once again respond with a 3-yard touchdown pass from Carson Palmer to Darrius Heyward-Bey.  The Steelers would kick a 33-yard field goal as time expired in the first half to give them a 17-14 lead.  The Steelers would begin the second half by driving down the field and scoring on a 22-yard touchdown pass to Mike Wallace.  But the Raiders would yet again respond with a 1-yard touchdown pass to Richard Gordon.  The Steelers would again drive down the field easily, but Antonio Brown would fumble the football in the endzone.  After review, it was determined that Brown had recovered his own fumble and the Steelers found themselves leading the game 31-21 with 1:31 left in the third quarter.  Early in the fourth quarter, Pittsburgh safety Ryan Mundy, playing for the injured Troy Polamalu, committed a helmet-to-helmet hit on Oakland receiver Heyward-Bey.  The hit knocked Heyward-Bey unconscious and he was taken to the hospital with a concussion and sprained neck.  (Mundy was not flagged for the illegal hit by the replacement referees, but would be fined by the NFL a few days later.)  The Steelers secondary issues from the past few years continued, as they could not stop Carson Palmer and the Raiders passing attack.  The Raiders would score on a 6-yard touchdown pass and a 32-yard field goal to tie the game at 31.  The Steelers had a chance to win the game late in the fourth quarter, but the Raiders defense held them to a 3-and-out and forced them to punt the ball back.  Palmer would again exploit Pittsburgh's suspect secondary and kicker Janikowski would kick a 43-yard field goal as time expired to give the Raiders a 34-31 victory over the Steelers, their first of the season.  The Steelers would head into their bye-week 1-2, and eventually ended up being the only AFC North team to lose to the Raiders.

Based on the above article, answer a question. How many yards was the first TD pass of the second half?
22