Function or not functional? Pls help tyyy

What is the name used to describe a graph where for some value of x, there exists 2 or more different values of y?

Jack has a piece of red ribbon that is two times as long as his piece of blue ribbon. he says that he can use two different equation to find out how long his piece of red ribbon is compared to his piece of blue ribbon is. is he correct? explain his reasoning

In a column proof the right column states your reasons