Solve the system $$\left\lbrace \begin{array}{r@{}r@{}r@{}r@{}r@{}r} x_1 & & +4 x_3 & + 3 x_4 & = & -18 \\ & x_2 & - 4 x_3 & - 2 x_4 & = & 19 \\ 2 x_1 & - 2 x_2 & +15 x_3 & + 10 x_4 & = & -68 \\ & - x_2 & +4 x_3 & + 8 x_4 & = & -1 \end{array}\right.$$ $x_1 =$
$x_2 =$
$x_3 =$
$x_4 =$