After a tough road loss to the Patriots, the Steelers traveled home to take on the Bills.  The Bills scored first in the first quarter when Dan Carpenter nailed a 20-yard field goal for a 3-0 lead and the only score of the quarter.  The Steelers however, responded by doing it big starting off in the 2nd quarter tying the game at 3 when Shaun Suisham nailed a 36-yard field goal.  They would increase their lead as Ben Roethlisberger found Jerricho Cotchery on a 5-yard TD pass giving them a 10-3 halftime lead.  After the break, the Steelers went back to work as Le'Von Bell ran for a 4-yard TD increasing their lead to 17-3.  They followed up in the 4th quarter with 2 Suisham field goals from 37 and 23 yards out for a lead of 20-3 and then 23-3 respectively.  The Bills finally managed to score a TD in the final seconds of the game when EJ Manuel found Chris Gragg on a 2-yard pass, making the final score 23-10 sealing the win for the Steelers improving themselves to 3-6.
Question: How many points was the Steelers' margin of victory?
Answer: 13