What is the domain of the function shown in the mapping?

{x | x = –5, –3, 1, 2, 6}
{y | y = –9, –6, 0, 2, 4}
{x | x = –9, –6, –5, –3, 0, 1, 2, 4, 6}
{y | y = –9, –6, –5, –3, 0, 1, 2, 4, 6}