\text { The matrix } \mathbf{A}=\left[\begin{array}{rrr} 3 & -1 & 2 \\ -7 & 3 & -4 \\ -2 & 2 & -4 \end{array} \mid \text { has an eigenvalue

} \lambda=4\right. \text { . } Find aneigenvector for this eigenvalue.