In order to list the ordered pairs, let's find each relation of input-output created by the arrows:
(-2, 15), (0, 10), (0, 20), (2, 5), (4, 20).
To be a function, every input must have only one corresponding output.
Looking at the mapping diagram and the ordered pairs, the input 0 has two corresponding outputs: 10 and 20.
Therefore the relation is not a function.
