Решение систем уравнений второй степени

Решите задачу:

$\left \{ {{y+x=-4} \atop {yx+7y=-4}} \right. \; \left \{ {{x=-4-y} \atop {y(-4-y)+7y=-4}} \right. \; \left \{ {{x=-4-y} \atop {-4y-y^2+7y+4=0}} \right. \; \left \{ {{x=-4-y} \atop {y^2-3y-4=0}} \right. \\\\y^2-3y-4=0\; ,\; \; y_1=-1,\; y_2=4\; (teorema\; Vieta)\\\\ \left \{ {{x_1=-3} \atop {y_1=-1}} \right. \; \left \{ {{x_2=-8} \atop {y_2=4}} \right.$