Umnichka1 X+y=6  ------------>x=y-6--------->x=y-6--------------------->x=y-6
x^2-y^2=12  ------>(y-6)^2-y^2-12=0---->y^2-12y+36-y^2-12=0------>-12y+24=0
-12y+24=0         x=y-6
-12y=-24           x=2-6
y=-24/-12           x=-4
y=2

1996sasha  x+y=6  
x^2-y^2=12
х=6-у
36-12у+у^2-y^2=12
-12у=-24
у=2
х+у=6
х+2=6
х=4