How does f (x) = 9x change over the interval from x = 4 to x = 5?

Answer: A

put x = 3 into f (x) = 6x and you get f (x) = 18

Put x = 4 into f (x) and you get f (x) = 24

Subtract those two. 24 - 18 = 6

Also, f (x) = 6x it will always be 6 away from the next x you put into the equasion.

Or better said, it will be 6 more from 6x, because you are changing the x to X+1, hence,

6 (x+1) = 6x + 6.

+6, it increases.