$$\left. \begin{array} { l } { x _ { 1 } + x _ { 2 } = 22 } \\ { x _ { 1 } + x _ { 3 } = 19 } \\ { x _ { 2 } - x _ { 3 } = 3 } \end{array} \right.$$
$x_{1}=19-x_{3}$
$x_{2}=x_{3}+3$
$x_{3}\in \mathrm{R}$
