Ineed ! pls me : )

question 16.

which of the sets of ordered pairs represents a function?

a = {(2, 7), (1, –5), (7, 2), (2, –9)}

b = {(5, 3), (–2, –9), (–3, 8), (9, 3)}

only a
only b
both a and b
neither a nor b