I think 2 equal ratios are called a <u>proportion</u>
Answer:

Step-by-step explanation:
The given function is
.
The domain refers to all values of x for which this function is defined.
Recall that: the domain of
is 
And we know
is the reciprocal of
.
Therefore the complement of the domain of
which is
is the domain of 
The price of the discount is $25 x 0.15 = $3.75
The price of the book with discount is $25 - $3.75 = $21.25
Correct answer is B
25 characters