The relationship below does not model a proportional relationship. This is due to the fact that when you divide each domain (another word for input, or x) by its range (another word for output, or y), each result it not similar.
For example:
12 / 8 = 1.5
24 / 24 = 1
36 / 32 = 1.125
and so on.
As you can see, the rate changes throughout the table and does not stay similar. Though, it would be proportional if, for example, each x / y were equal to 1.5