y=2x+4

10x-5y=-20

i know using the substitution method plays out like so...

10x-5(2x+4)=-20

10x-10x-20=-20

10x-10x=0

0=0

I have to express the answer in interval notation....how would I do that, and since the answer is 0=0 is their a value for x and y at all