Which one of the relationships described is not proportional?

a.
Cedrick earns $9.75 for each day he pet-sits; is the relationship between the money he earns and the days he works proportional?

b.
Marianne is 15 years old and her brother is 5 years old; is the relationship between their ages proportional?

c.
The length of the side of a square and its perimeter; is the relationship between the measurements proportional?

d.
A car travels at a constant speed of 35 miles per hour is the relationship between the distance and the time proportional?