What is x2 + 6x = x2 – 6x as a system?

A.) y = x2 + 6x
y = x2 – 6x

B.) y = –x2 + 6x
y = x2 – 6x

C.) y = –x2 – 6x
y = x2 – 6x
And can you please work it out because i am so confused?