Помогите срочно с математикой: 2,3,4

Вариант 1
2) $\left \{ {{2x-y} =1\atop {x+y=-4}} \right. \\ \left \{ {{2x-y} =1\atop {x=-4-y}} \right. \\ \left \{ {{2(-4-y)-y} =1\atop {x=-4-y}} \right. \\ \left \{ {{-8-3y} =1\atop {x=-4-y}} \right. \\ \left \{ {{-3y} =9\atop {x=-4-y}} \right. \\ \left \{ {{y} =-3\atop {x=-4-y}} \right. \\ \left \{ {{y} =-3\atop {x=-4+3}} \right. \\ \left \{ {{y} =-3\atop {x=7}} \right. \\$