Let $$\vec{x} = \left[\begin{array}{c} -9\cr -6\cr 3\cr 0 \end{array}\right] \ \mbox{ and } \ \vec{y} = \left[\begin{array}{c} 5\cr 2\cr 5\cr 6 \end{array}\right].$$ Use the Gram-Schmidt process to determine an orthonormal basis for the subspace of ${\mathbb R}^4$ spanned by $\vec{x}$ and $\vec{y}$.