Решительно систему -6x+y=21 6x-11y=-51

Решите задачу:

$\left \{ {{-6x+y=21} \atop {6x-11y=-51}} \right.$
$\left \{ {{y=21+6x} \atop {6x-11y=-51}} \right.$
$\left \{ {{y=21+6x} \atop {6x-11(21+6x)=-51}} \right.$
$\left \{ {{y=21+6x} \atop {6x-231-66x=-51}} \right.$
$\left \{ {{y=21+6x} \atop {-60x-231=-51}} \right.$
$\left \{ {{y=21+6x} \atop {60[=51-231}} \right.$
$\left \{ {{y=21+6x} \atop {60x=-180}} \right.$
$\left \{ {{y=21+6x} \atop {x=-180:60}} \right.$
$\left \{ {{y=21+6x} \atop {x=-3}} \right.$
$\left \{ {{y=21+6*(-3)} \atop {x=-3}} \right.$
$\left \{ {{y=21-18} \atop {x=-3}} \right.$
$\left \{ {{y=3} \atop {x=-3}} \right.$