Здравствуйте умоляю помогите с алгеброй (на картинке)

1.(3;1)-не явл. [latex] \left \{ {{x+y=12}, \atop {x-y=2};}\right. \left \{ {{3+1 \neq 12} \atop {3-1=2}} \right. [/latex] (7;5)-явл. [latex] \left \{ {{7+5=12}, \atop {7-5=2};} \right. \left \{ {{12=12} \atop {2=2}} \right. [/latex] 3.[latex] \left \{ {{7x-10y=18},*2 \atop {-2x+11y=3};*7} \right. \left \{ {{14x-20y=36,} \atop {-14x+77y=21;}} \right. \left \{ {{57y=57} \atop {-2x+11y=3}} \right. \left \{ {{y=1} \atop {-2x=-8}} \right. \left \{ {{y=1} \atop {x=4}} \right. [/latex] Ответ:(4;1)-В

Решение во вложении: