\text { 3. Write }\left[\begin{array}{l} 6 \\ 4 \\ 5 \end{array}\right] \text { as a linear combination of the vectors }\left[\begin{array}{c} 3 \\ 1 \\ -1 \end{array}\right] \text { and

}\left[\begin{array}{l} 1 \\ 4 \\ 2 \end{array}\right], \text { or determine that it is not possible. }