Exercise 4.3.20

The matrix $A$ has columns $1,1,1$ and $-1,1,2$. If $b=A\hat{x}=(5,13,17)$ then $\hat{x}=(9,4)$ and $e=0$ since $b=9($ column 1 $)+4($ column 2 $\text{)}$ is in the column space of $A$.