I have two possible answers that I came up with for the basis of the column space for the matrix $\begin{bmatrix}2& 4\\ 4 &8\\ 1 & 2\\ 0 &0\end{bmatrix}$ ..
Is it a matrix with the bottom row removed and e1 and e2 added $\begin{bmatrix}2& 0 & 0\\ 4 &1 & 0\\ 1 & 0 & 1\end{bmatrix}$
or does the bottom row stay $\begin{bmatrix}2& 0 & 0 & 0\\ 4 &1 & 0 &0\\ 1 & 0 & 1 & 0\\ 0 & 0 & 0& 1\end{bmatrix}$ ?