I'm not sure what your book is saying about the matter but a cell phone is not usually an essential expense. If it is saying it is though, it would be an essential flexible expense.
Answer:
Hence, the model that best represents the data is:

Step-by-step explanation:
We are given a table that shows the estimated number of lines of code written by computer programmers per hour when x people are working.
We are asked to find which model best represents the data?
So for finding this we will put the value of x in each of the functions and check which hold true that which gives the value of y i.e. f(x) as is given in the table:
We are given 4 functions as:
A)

B)

C)

D)

We make the table of these values at different values of x.
x A B C D
2 66.66 49.3 52.5 50
4 94.57 71.44 106.3 104
6 134.14 103.57 160.1 158
8 190.27 150.14 213.9 212
10 269.91 217.64 267.7 266
12 382.85 315.5 321.5 320.
Hence, the function that best represents the data is:
Option C.
y=26.9x-1.3
the answer should be 780π
Answer:
d. can be equal to the value of the coefficient of determination (r2).
True on the special case when r =1 we have that 
Step-by-step explanation:
We need to remember that the correlation coefficient is a measure to analyze the goodness of fit for a model and is given by:
The determination coefficient is given by 
Let's analyze one by one the possible options:
a. can never be equal to the value of the coefficient of determination (r2).
False if r = 1 then 
b. is always larger than the value of the coefficient of determination (r2).
False not always if r= 1 we have that
and we don't satisfy the condition
c. is always smaller than the value of the coefficient of determination (r2).
False again if r =1 then we have
and we don't satisfy the condition
d. can be equal to the value of the coefficient of determination (r2).
True on the special case when r =1 we have that 
For this case what we should do is take into account the following conversion:

We then have the following number:

Applying the given conversion we have:

By doing the corresponding calculation we have that the standard form is given by:
Answer:
4540 million in standard form is: