Please give me the correct answer.

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

Researchers were interested in whether relaxation training decreases the number of headaches a person experiences. they randomly assigned 20 participants to a control group or a relaxation training group and noted the change in number of headaches each group reported from the week before training to the week after training. which statistical analysis should be performed to answer the researchers' question?

Prove that the value of the expression 7^8–7^7+7^6 is divisible by 43.