The Lions traveled west in week 3 to play their division rival the Green Bay Packers. The Packers got on the board first with a 14-yard touchdown pass from Aaron Rodgers to Davante Adams. The Lions responded with a 42-yard field goal from Matt Prater. Green Bay accumulated a big lead with two touchdown catches by Jordy Nelson for eight and later 17 yards, one by Richard Rodgers from two-yards, as well as a 36-yard field goal from Mason Crosby. Detroit made the halftime score 31-10 after Marvin Jones caught a 17-yard touchdown catch from Matthew Stafford. After the break, the Lions attempted a comeback with touchdown catches by Anquan Boldin and Marvin Jones, from two and 45-yards respectively, as well a 50-yard Prater field goal. Despite only allowing a 46-yard Packers field goal in the second half, the Lions came up short, losing  27-34.
Question: How many points were the Packers winning by at halftime?
Answer: 21