X+ y = k
x - y = k

the solution to the system shown is

Hello,
x+y=k
x-y=k
==>2x=2k ==>x=k
y=k-k=0

Sol={(k,0)}

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.

I’ll you if you answer my questions!