Find the value of \( x_{2} \) in the unique solution of the given linear system. \[ \begin{array}{l} 3 x_{1}-3 x_{2}-3 x_{4}=9 \\ -x_{1}+2 x_{3}+x_{4}=2 \\ x_{1}+3 x_{3}=4 \\ -2 x_{2}+3 x_{3}+3 x_{4}=