For the matrix $A$ below, find a set of vectors $S$ so that the span of $S$ equals the null space of $A$, $\spn{S}=\nsp{A}$. \begin{equation*} A= \begin{bmatrix} 1 & 1 & 6 & -8\\ 1 & -2 & 0 & 1\\ -2 & 1 & -6 & 7 \end{bmatrix} \end{equation*}