Find the set of solutions for the linear system

$$\begin{array}{rcrcrcrcr}2 x_1 & + & 5 x_{2} & - & x_{3} & + & x_{4} & = & 18 \\ & - & x_{2} & - & 7 x_{3} & - & 12 x_{4} & = & -7 \\ & & & & 3 x_{3} & - & x_{4} & = & 11\end{array}$$ If your answer includes any arbitrary parameters name them s1, s2, etc., as needed.

$(x_1, x_2, x_3,x_4) = \bigg($ , , , $\bigg)$