Тока четные...............и граф

Решите задачу:

$2)\; \; \left \{ {{y=-3x} \atop {y-x=-4}} \right.\; \left \{ {{y=-3x} \atop {y=x-4}} \right.\; \; \Rightarrow \; \; (1,-3)\\\\4)\; \; \left \{ {{y=3x} \atop {4x-y=3}} \right. \; \left \{ {{y=3x} \atop {y=4x-3}} \right.\; \; \Rightarrow \; \; (3,9)\\\\6)\; \; \left \{ {{y=x-1} \atop {y+x=1}} \right. \; \left \{ {{y=x-1} \atop {y=-x+1}} \right.\; \; \Rightarrow \; \; (1,0)$