Chapter 2.9, Problem 13E

In Exercises 13 and 14, find a basis for the subspace spanned by the given vectors. What is the dimension of the subspace?

13. $\left[\begin{array}{l}1\\ -3\\ 2\\ -4\end{array}\right]$, $\left[\begin{array}{l}-3\\ 9\\ -6\\ 12\end{array}\right]$, $\left[\begin{array}{l}2\\ -1\\ 4\\ 2\end{array}\right]$, $\left[\begin{array}{l}-4\\ 5\\ -3\\ 7\end{array}\right]$