Ok, so
If there's a proportional relationship, there should be a ratio between the quantity of popcorn and the time it takes to make it.
So, we can write this as:
[tex]\begin{gathered} \frac{14}{2.5}\questeq\frac{16}{3.5} \\ 5.6\ne4.571 \end{gathered}[/tex]As there is not a ratio, there is not a proportional relationship.