Marsha scored 92, 81, 98, and 84 on his first four Math quizzes. What score does Marsha need to get on her fifth quiz to have an average of exactly 90 on her Math
quizzes?

answer: i think it is (1,-2)

sample answer: you can determine whether each element of the domain is paired with exactly one element of the range. for example, if given a graph, you could use the vertical line test; if a vertical line intersects the graph more than once, then the relation that the graph represents is not a function.