Answer:
Associative.
Step-by-step explanation:
In addition and multiplication, it does not matter which two numbers you put together first. On the left aide 6 is associated with 3. On the right side 3 is grouped with 7. It doesn't matter where 3 goes. You still get the same answer.
(6 + 3) + 7 = 6 + (3 + 7)
9 + 7 = 6 + 10
16 = 16
For this case we have:
Cost of manufactures of T-shirts 
where x represents the number of T-shirts
Part A:
Substituting
in the total cost equation you have to:

Thus, the cost of 8 shirts will be 
Part B:
If
then

Thus, the cost of 12 shirts will be 
Answer:

1,2,3,4 are the domain. The x column is always the domain.
When you expand the equation, you will have
9x + 9=25 + x
Next you have to collect like terms
+x will go over the equality sign to become -x. The same applies to +9
9x - x=23 - 9
9x minus x is 8x
8x=14
Divide both sides by 8
x=14/8
You will have 1 6/8
6 is the remainder while 1 is the number of times 8 divided 14.
In decimal, it will be 1.75
Hope that helped. Good luck