The table below would represent a proportional relationship except for one y-value. Identify which y-value prevents the table from representing a proportional relationship. Then, select the value that would make the table proportional.

X 1.5, 2, 4, 4.5, 7
Y 6, 8, 16, 16.5, 28

Alternative values 17, 18, 18.5, 19.5, 20