Как решить ??????помогите

Решите задачу:

$a)\; \; y(x-2)-x(y+1)=2-3(x-2)\; \; \Rightarrow \\\\\underline {yx}-2y-\underline {xy}-x=2-3x+6\; ,\; \; -2y-x+3x=2+6\; ,\\\\2x-2y=8\; |:2\\\\x-y=4\\\\b)\; \; y(x+5)-y(x-2)=-42+4(x+5)\; \; \Rightarrow \\\\\underline {yx}+5y-\underline {yx}+2y=-42+4x+20\; ,\; \; 5y+2y-4x=-42+20\; ,\\\\7y-4x=-22\\\\c)\; \; \left \{ {{x-y=4} \atop {7y-4x=-22}} \right.\; \; \left \{ {{x=y+4} \atop {7y-4(y+4)=-22}} \right.\; \; \left \{ {{x=y+4} \atop {7y-4y-16=-22}} \right. \\\\\left \{ {{x=y+4} \atop {3y=-6}} \right.\; \; \left \{ {{x=-2+4} \atop {y=-2}} \right. \; \; \left \{ {{x=2} \atop {y=-2}} \right.\\\\Otvet:\; \; (2,-2)$