Помогите решить пожалуйста срочно

Решите задачу:

$\left \{ {{y + x - 4 = 0} \atop {-x+2y+1=0}} \right. \\\left \{ {{x =4-y} \atop {-(4-y)+2y+1=0}} \right. \\\left \{ {{x=4-y} \atop {-4+y+2y+1=0}} \right. \\\\\left \{ {{x=4-y} \atop {-3+3y=0}} \right. \\\left \{ {{x=4-y} \atop {3y=3}} \right. \\\left \{ {{x=4-y} \atop {y=1}} \right. \\\left \{ {{x=3} \atop {y=1}} \right.$