Алгебра 7 класс, решите пожалуйста.

Решите задачу:

$\left \{ {{y=7-2x} \atop {5x-2y=40}} \right. \\ \left \{ {{y=7-2x} \atop {5x-2(7-2x)=40}} \right. \\ \left \{ {{y=7-2x} \atop {5x-14+4x=40}} \right. \\ \left \{ {{y=7-2x} \atop {9x-14=40}} \right. \\ \left \{ {{y=7-2x} \atop {9x=54}} \right. \\ \left \{ {{y=7-2x} \atop {x=6}} \right. \\ \left \{ {{y=7-2*6} \atop {x=6}} \right. \\ \left \{ {{y=-5} \atop {x=6}} \right.$