Do quarterbacks matter? How important is the quarterback's skill to the success of an NFL foot- ball team? One way to measure a quarterback's effectiveness is with the "quarterback rating," a complex calculation based on passing accuracy and yardage, touchdown passes, and interceptions. If we create a least-squares linear regression model for AFC teams relating y = team wins during the 2013 season to x = the overall quarterback rating for the team's quarterbacks, we get the following residual plot. 3 2- 1 Residual -1 -2- -3 -5 60 70 80 90 100 Quarterback rating 110 120 (a) Use the residual plot to determine whether the regression model is appropriate. (b) Interpret the value s = 2.473 for this model. (c) Interpret the value = 0.457 for this model.