TO determine if the variables x and y are a function, i.e. that y varies in function of x you have to determine the "inputs" and "outputs" of the table.
-If for every "input", that is, every value of x there is only one "output" or value of y, then you can clasify them as a function.
-If for at least one "input" there is more than one "output", then the data in the table cannot be classified as a function.