Exercise 3.5.2

$A$ : Row space basis = row $1=(1,2,4)$; nullspace $(-2,1,0)$ and $(-4,0,1)$; column space basis $=$ column $1=(1,2)$; left nullspace $(-2,1)$. $B$ : Row space basis $=$ both rows $=(1,2,4)$ and $(2,5,8)$; column space basis $=$ two columns $=(1,2)$ and $(2,5)$; nullspace $(-4,0,1)$; left nullspace basis is empty because the space contains only $y=0$ : the rows of $B$ are independent.