What is the domain of the given function?

{x | x = –6, –1, 0, 3}
{y | y = –7, –2, 1, 9}
{x | x = –7, –6, –2, –1, 0, 1, 3, 9}
{y | y = –7, –6, –2, –1, 0, 1, 3, 9}