$\left(\begin{array}{c}6\\ 3\\ 1\\ 1\end{array}\right)+\<\left(\begin{array}{c}2\\ 0\\ 1\\ 0\end{array}\right)-\left(\begin{array}{c}6\\ 3\\ 1\\ 1\end{array}\right),\left(\begin{array}{c}1\\ 3\\ 3\\ 1\end{array}\right)-\left(\begin{array}{c}6\\ 3\\ 1\\ 1\end{array}\right)>=\left(\begin{array}{c}6\\ 3\\ 1\\ 1\end{array}\right)+\<\left(\begin{array}{c}-4\\ -3\\ 0\\ -1\end{array}\right),\left(\begin{array}{c}-5\\ 0\\ 2\\ 0\end{array}\right)>\text{.}$