How we can differentiate between direct proportion and inverse proportion?

Please check explanations for answer

Step-by-step explanation:

Here, we want to differentiate between inverse and direct proportion

Let x and y be two quantities

If they are directly proportional;

x/y = k

x = ky

where k is proportionality constant

If inversely;

xy = k

In verbal terms;

For direct proportionality, when one value increase, the other too does so and vice versa

For inverse, when one value inverse, the other decrease

i believe it is c.y = 9x

rise over run. 9 units up over 1 unit right or 9/1