It is called direct variation.
That is known as a unit rate.
A ratio uses division to compare two quantities.
A rate is a ratio of two quantities: miles per hour, calories per cookie, dollars per person, ... a unit rate just specifies the units (miles, hours) of the two quantities.
The answer is proportional.
The diameter and circumference of a circle.
Two quantities are said to be proportional if they vary in such a way that one of the quantities is a constant multiple of the other, or equivalently if they have a constant ratio.
It is a direct proportion.
rate is a ratio that compares two quantities of different units
They have a constant rate or ratio.