Find the basis for and the dimension of $\displaystyle W=span(\mathbf{v_1, v_2, v_3})$, where

$\displaystyle \mathbf{v_1}=\begin{pmatrix}1\\ 2\\ 3\end{pmatrix}, \mathbf{v_2}=\begin{pmatrix}1\\ 1\\ -1\end{pmatrix}, \mathbf{v_3}=\begin{pmatrix}-1\\ 0\\ 5\end{pmatrix}$

I'm not too sure how to start this question off