Coming off their Bye Week, the Dolphins would get their second win of the 2006 season against the previously undefeated Chicago Bears at Soldier Field.  Just as the 1985 Dolphins ended the Bears' attempt at a perfect season (they finished 18-1), this year's Dolphins again protected the 1972 Perfect Season on their own.  QB Joey Harrington was 16/32, for 137 yards, and 3 touchdowns, despite 2 interceptions.  The Dolphins fumbled twice, but recovered both times, and the Bears also fumbled twice, but both times Miami came away with the ball.  The Dolphins were also able to capitalize on 3 interceptions on Rex Grossman passes.  Ronnie Brown rushed for a career-high 157 yards, carrying 29 times.  Jason Taylor forced a fumble and returned an interception 20 yards for a touchdown, helping Miami in its 31-13 victory.  The spirit of the 1972 Dolphins looked alive and well as Miami improved to 2-6 on the year.
Question: How many points did the Dolphins win by?
Answer: 18