Ответ:

[tex]\left \{ {{\frac{x}{6}+\frac{y}{6}=2|*(-6)} \atop {\frac{x}{20}+\frac{y}{10}=2|*20}} ight. \\\left \{ {{-x-y=-12} \atop {x+2y=40}} ight. +\\-x+x-y+2y=-12+40;y=28\\-x-y=-12;-x-28=-12;-x=16\Rightarrow x=-16[/tex]

Ответ: (-16;28).