33 Minutes i think, Sorry if im wrong
10:4, 15:6, and 20:8. All you do is add the original ratio to its self
Cross multiplication will help find the value of x

9*2=18
3*z=3z
Now we have :
3z=18
Divide both sides by 3 to isolate z
Final answer: z=6
Rate of change is used to mathematically describe the percentage change in value over a defined period of time. (I looked that up)
So the rate of change is the slope and slope is the ratio of change between any 2 points on a line.
Slope measures the steepness of a line.
Slope is the ratio of the vertical change, called the rise, to the horizontal change called the run between any 2 points on the line.
Slope is written as a fraction in simplest form. 5/10=1/2
Variable for slope: M.
Reply for any more questions, also sorry for a slow response. I thought a lot.