Function: Each x maps to one single y, no matter that is the same y.

Not Function: For x = -4 there are infinitely many y's.

Not Function: x = 3 maps to four y's.

Function: Each x maps to one single y, no matter that is is the same y = 2.

Not Function, two sets of points have the same x entry 4, mapping once towards 0 and once to (-6).

Function: Each entry in the top row is different.

Function: There are no two parenthesis with the same x.

Not Function. On the top row with the input, x = -1 appears twice mapping to two different y values.