Hmm question is a little confusing but fractions can be represented as division or a part of somthing, like 4 pieces of an 8 slice pizza, or you have 8 peices of pizza and you divide them by 4. Im pretty sure a rational number is any number that can be representated as a fraction. an irrational number is something you cant express as a fraction like the square root of a number or pi.
A ) The domain:

x ≤ -4 and x≥ 4 or: x ∈ ( - ∞ , - 4 ) ∪ ( 4 , + ∞ )
b ) f ` ( x ) =

c ) The slope of the line normal to the graph at x = 5
m = -1 / f `(x)
f ` ( x ) =
m = - 3/34