Final answer:
The ratios of the number of people to the number of rollercoaster cars are proportional because all the given ratios simplify to 6:1.
Step-by-step explanation:
To determine if the ratios of the number of people to the number of rollercoaster cars are in a proportional relationship, we must see if the ratios are equivalent. If we look at the provided ratios, 18:3, 30:5, 36:6, and 48:8, we see that when simplified all become 6:1. This indicates that the relationship is indeed proportional because the same ratio is maintained throughout all given pairs.