Answer:
First Box: Factor by difference of squares
Second Box: It has all perfect squares
Third Box: see my work
Step-by-step explanation:
We have the equation 
Before we do anything, let us bring all of the terms to the left side

Now that we have moved the terms to one side, it is clear that we have a difference of squares.
-Work-

-

-

The sum of angle AOB and angle BOC is equal tot he angle of AOC so
6x+5 +4x-2 = 8x+21
10x+3=8x+21
Subtract three and 8x from both sides
2x=18
Divide by two
x=9
Hope this helped!
If you are satisfied please like
Answer:

Step-by-step explanation:
general slope intercept equation of a straight line is given as

where m is slope and b is y-intercept
here
and

Question 1:
F(x) and g(x) are like variables, just plug into the equation.
f(x) + g(x) = (x + 6) + (12x - 7)
x+6+12x-7 = 13x-1
Question 2: f(3) + g(-1)
You plug in the x-values into the equation, and then take the answer and add them together.
f(3) = 3+4
g(-1) = 12(-1)-6
f(3) = 7
g(-1) = -18
7 + (-18) = -11
Question 3:
This is similar to question 1, plug in the variables and simplify.
9x - (7x+3)
Remember to distribute the "-"
9x - 7x - 3
2x - 3