Нужно решение...........

$7)\; \; y=-3x+b\\\\M(-2,4):\; \; 4=-3\cdot (-2)+b\; ,\; 4=6+b\; \; \to \; \; b=-2\\\\Otvet:\; \; B\; .\\\\8)\; \; y=kx+b\; \; ,\; \; A(0,3)\; ,\; \; B(1,2)\\\\\left \{ {{3=k\cdot 0+b} \atop {2=k\cdot 1+b}} \right. \; \left \{ {{b=3} \atop {k=2-b}} \right. \; \left \{ {{b=3} \atop {k=-1}} \right. \\\\Otvet:\; \; C\; .$

$9)\; \; \left \{ {{3x+2y=5} \atop {-5x+2y=45}} \right. \ominus \left \{ {{2y=5-3x} \atop {3x+5x=-40}} \right. \; \left \{ {{2y=5-3x} \atop {x=-5}} \right. \; \left \{ {{2y=20} \atop {x=-5}} \right. \; \left \{ {{y=10} \atop {x=-5}} \right. \\\\x+y=-5+10=5$

Ответ: г) .

$10)\; \; \left \{ {{12x-7y=2} \atop {4x-5y=6\, |\cdot (-3)}} \right. \oplus \left \{ {{12x=2+7y} \atop {8y=-16}} \right. \; \left \{ {{12x=-12} \atop {y=-2}} \right. \; \left \{ {{x=-1} \atop {y=-2}} \right. \\\\y-x=-2-(-1)=-2+1=-1\\\\Otvet:\; \; a)\; .$