Find the inverse of the linear transformation $$\begin{array}{r@{}r@{}r@{}r@{}r} y_1 & = & 2 x_1 & - 4 x_2 & + 7 x_3 \\ y_2 & = & 4 x_1 & - 7 x_2 & + 10 x_3 \\ y_3 & = & x_1 & - 2 x_2 & + 3 x_3 \end{array}$$
$x_1=$ $y_1+$ $y_2+$ $y_3$,
$x_2=$ $y_1+$ $y_2+$ $y_3$,
$x_3=$ $y_1+$ $y_2+$ $y_3$.