Read this article and answer this question The Steelers traveled back up north to Cleveland to take on the Browns.  In the first quarter, the Steelers score the only 3 points as Shaun Suisham nailed a 20-yard field goal to take a 3-0 lead.  The Browns however scored 21 unanswered points in the 2nd quarter when Isaiah Crowell ran for a 5-yard TD to take a 7-3 lead followed by Brian Hoyer hooking up with Jordan Cameron on a 51-yard TD pass for a 14-3 lead before finally Ben Tate ran for an 8-yard TD and took a 21-3 lead at halftime.  The Browns continued their domination day in the 3rd quarter when Billy Cundiff kicked a 40-yard field goal for the only score of that quarter.  In the 4th quarter, they sealed the game when Ben Tate ran for a 1-yard TD making the score 31-3.  The Steelers drove down the field and Ben Roethlisberger found Lance Moore on a 26-yard TD pass for a final score of 31-10. With the loss, the Steelers fell to 3-3 and last place in the AFC North.
How many points behind were the Steelers at halftime?
18