Answer:
Option b - Subtract
Step-by-step explanation:
Given : Expression 
To find : Which operation should be completed first in the expression below?
Solution :
P - Parentheses
E - Exponent
D - Divide
M - Multiplication
A - Addition
S - Subtraction
In the first step we solve the bracket in the expression 
So, we do subtraction i.e. 12-8=4
Therefore, option b is correct.
Answer:
C) y=13+15x
Step-by-step explanation:
y=13+15x
Solution: We are given below data:

Now to find the mean deviation, we use the below formula:

Where:
represents the summation
X, represents the observation.
represents the mean
N represents the number of observation.


Therefore, the mean deviation is:

= 4
Where <em>x </em>is the number of books sold, <em>i </em>is income, and <em>c </em>is cost:
<em>c = 4x + 3500 </em> ($4 per book plus the 3500 flat marketing fee)
<em>i = 15x </em>($15 per book)
You are looking for the point where these intersect: the intersection is where the income is equal to the cost, and at any point after that the income is greater than the cost. So, set the equations equal to each other:
<em>4x + 3500 = 15x </em>
subtract 4x from both sides
<em>3500 = 11x</em>
divide both sides by 11
<em>x = 318.181818</em>
So, you would have to sell a minimum of 319 books in order to make a profit.