Which of the following relations represent a function?

{(-1,-,,7)}
{(-3,,-,7)}
{(-1,,,5)}
{(-1,,,7)}

You must find the set that doesn't have a repeating x value.

looking at the first set you can see that there are two 3's
looking at the second set you can see that there are also tow 3's
looking at the third set you can see that there are two -1's
looking at the fourth set you can see there is nothing that is repeating in the x values. So the fourth set would be your answer.