A regression was run to determine if there is a relationship between hours of TV watched per day (x) and number of situps a person can do (y).

The results of the regression were:

y=ax+b a=-0.864 b=37.082 r^{2}=0.850084 r=-0.922

Use this to predict the number of situps a person who watches 4.5 hours of TV can do (to one decimal place.

I plugged in 4.5 into the equation and got 40.9. The answer is wrong. What am I doing wrong?