Let $A = \left[{\begin{matrix}2 & 4 & 2 \cr 3 & 9 & 18 \cr 4 & 10 & 16 \cr \end{matrix}}\right]$.

We want to determine if the columns of $A$ span ${\mathbb R}^3$.

To check this we add times the first row to the second.
We then add times the first row to the third.
We then add times the new second row to the new third row.
We conclude that

A. The columns of $A$ do span ${\mathbb R}^3$.
B. The columns of $A$ do not span ${\mathbb R}^3$.
C. We cannot tell if the columns of $A$ span ${\mathbb R}^3$.