система х+у=10 у-х=4 помогите

[tex] \left \{ {{x+y=10} \atop {y-x=4}} \right. \\ \left \{ {{y=10-x} \atop {-x+10-x=4}} \right. \\ \left \{ {{y=10-x} \atop {-2x=-6}} \right. \\ \left \{ {{x=3} \atop {y=7}} \right. [/tex]