Помогите пожалуйста!!СРОЧНО! Тема-способ подстановки:

a) могу решить только 1 [latex] \left \{ {{x-5y=7} \atop {2x-5y=9}} \right. [/latex] [latex] \left \{ {{x=7+5y} \atop {2(7+5y)-5y=9}} \right. [/latex] [latex] \left \{ {{x=7+5y} \atop {14+10y-5y=9}} \right. [/latex] [latex] \left \{ {{x=7+5y} \atop {14+5y=9}} \right. [/latex] [latex] \left \{ {{x=7+5y} \atop {5y=9-14}} \right. [/latex] [latex] \left \{ {{x=7+5y} \atop {5y=-5}} \right. [/latex] [latex] \left \{ {{x=7+5y} \atop {y=-1}} \right. [/latex] [latex] \left \{ {{x=7+5(-1)} \atop {y=-1}} \right. [/latex] [latex] \left \{ {{x=7-5} \atop {y=-1}} \right. [/latex] [latex] \left \{ {{x=2} \atop {y=-1}} \right. [/latex]