Find a basis of the given subspace by deleting linearly dependent vectors.

$S$ = span of $\Bigg \lbrace \left[\begin{array}{c}10\\-6\\\end{array}\right]$, $\left[\begin{array}{c}-21\\12\\\end{array}\right] \Bigg \rbrace$.

A basis is $\Bigg \lbrace$$\left[\Rule{0pt}{2.4em}{0pt}\right.$$\left]\Rule{0pt}{2.4em}{0pt}\right.$, $\left[\Rule{0pt}{2.4em}{0pt}\right.$$\left]\Rule{0pt}{2.4em}{0pt}\right.$ $\Bigg \rbrace$.