2.
(a) No two ordered pairs have the same x-coordinate. That makes it a function.
(b) If the same x-coordinate appeared twice. For example, if the last point were replaced with point (4, 21), then it would not be a function since now there are two points with the same x-coordinate, 4.
(c) For each point, multiply x by 2. Then subtract 1. You will get the correct y-coordinate. The function is:
f(x) = 2x - 1
