Given the values on table A and table B, notice that on table A, if we look at the x column, we can see that the values are 0, 2, 2, and 3.
We know that a relationship between the elements of some set A and some set B is a function if every element of the domain (set A or the elements of the x column) is related with only one member of the codomain (set A or the elements or the y-column)
Since table A has an element that repeats (2), this means that this element is related with two different elements of the codomain, which cannot happen with a function.
Therefore, table A does not represent a function and table B does represent a function