I'm trying to do a Least Squares best fit for {1,2},{2,1},{3,3}. Unfortunately, my final formula continues to be wrong. 

As my final formula, I'm getting $y=\frac{1}{7}+\frac{13}{14}x$ - instead of - $y=0.5x +1$.

Because something obviously goes wrong while calculating $b$, I have attached my notes for that part. I tried to make it as clear as possible.

![Link to image](https://i.imgur.com/yQf631Q.jpg)

I really hope someone can help me out, thank you so much in advance!