Sorry I don’t know the answer and the question to
Answer:
tu debes de saber por qué si yo lo sé tú también no es verdad
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:
This is an example of
C. simultaneous causality.
Step-by-step explanation:
Simultaneous causality eliminates the conclusion that is often taken for granted to the effect that one variable is a response variable while the other is an explanatory variable because the two variables, the price and the number of shares, influence each other at the same time. When more shares are traded than demanded in the stock market in any day, the price tends to go down, and vice versa.