Hey! I'm not an expert in maths, but i came up with this.

a) If i understand it right you need to create a function for f/g

f/g = (-3x + 1)/(-5x + 6) = -1 * (3x - 1)/ -1 * (5x - 6) = (3x - 1)/(5x - 6)
This is the simplest form i can get it to.
x can't be equal to 1.2, since then 5 * 1.2 = 6 and 6 - 6 = 0, and you can't divide by 0.

b) If I understand it right, I can answer with an expression

Avg. is: delta y/delta x, so (highest Y - lowest Y)/(highest X - lowest X) =
(k(h - 1) - k(-1))/(h -1 - (-1)) = (k(h - 1) - k(-1))/h = (k(h - 1) -1)/h
This is the simplest form i can get it to. h -1 - (-1) is H because: - (-1) is +1 and -1 + 1 is 0, which we can ignore. H can't equal to zero is right as stated in the exercise.

c) If I understand right I can answer with an expression

Same.
Avg. = delta Y / delta X = (g(h) - g(0))/(h - 0) = (g(h) - g(0))/h = (g(h))/(h)
g(0) = 0, this way we can ignore this, because: 0^2 = 0, 0*9 = 0

Sorry if I did something wrong English isn't my main language.

Legend

/ means division
- means subtraction
* means multiplication
+ means add
delta means it's a differential value (highest value - starting point)
Let me know if this is what you want, or you can't understand this!