The answer would be graph x. A function must be that one x value should only have one y value. graph w doesn't work since when you plug in 0, you get two y's. same thing with z. Y doesn't work since at x value of 3, it curves back so x value 2 has 2 y's. X is the only one that each x value has only one y.
For a relationship to be a function, every input has exactly one output, so for every x value there is only one value.
If you look at answer's w and z for x=1 there is two y values, therefore they are not functions, letter Y is tricky. Even though every x value has only one y value, If you were to extend the graph x=0 would have more than one y values.
That leaves X. If you extend the graph of X every x value will only have one y value so it is a function
