Answer:
Part A) see the explanation
Part B) 
Step-by-step explanation:
Part A)
we know that
A relationship between two variables, x, and C, represent a proportional variation if it can be expressed in the form
or 
Let
C ---> is the total cost (represent the output or dependent variable)
x ----> is the number of books (represent the input or independent variable)
In this problem
we have a proportional relationship between the variables x and C
Part B) we know that
The linear equation is given by

The constant of proportionality k is the same that the slope or unit rate of the linear equation
In this problem the constant k is given

so

For x=12 books
substitute in the equation and solve for C

In function notation

Answer: independent variable: time (t). Dependent variable: distance (d).
Step-by-step explanation: an independent variable is a variable whose variation does not depend on that of another. In the given problem, the independent variable is time, because time will pass by no matter what (without depending in any other variable). The dependent variable in this case is the distance, because how far Jillian goes, depends on how much time she expends walking and jogging.
This is my explanation thus sucks and half the timem you guys dont even have the right answer . So this is my answer for you at leatst try to get it tight because if you dont try you wont suceed
ANSWER
The domain of the function is

or
[-3,6]
EXPLANATION
The domain of a function refers to the values of x for which the function is defined.
From the graph, we can see that the function begins at (-3,6) and ends at (6,-4).
Therefore the function is defined for x=-3 to x=6.
Hence the domain of the function is

or
[-3,6]
Answer:
15.
Step-by-step explanation:
3.75 / 25 = 15.