A proportional relationship is in the form of y=kx where k is the proportionality constant.
From the given options:
Consider the pairs (x,y) in Option D
(4,8),(7,14)(12,24),(15,30)
When y=8, x=4, Substituting into y=kx, we have: 8=4k and k=2
When y=14, x=7, Substituting into y=kx, we have: 14=7k and k=2
When y=24, x=12, Substituting into y=kx, we have: 24=12k and k=2
When y=30, x=15, Substituting into y=kx, we have: 30=15k and k=2
We can see that the proportionality constant is equal for the four pairs. Therefore, the set of pairs in Option D represents a proportional relationship.
The only thing I can think of to rewrite this is either 8+72t or changing the variable to a different letter. The expression is already in its simplest form.