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:

Answer:
y = x-4
Step-by-step explanation:
y = -x-5
Slope of line is -1.
Slope of perpendicular to line is 1.
Point-slope equation for line of slope 1 that passes through (6,2):
y-2 = 1(x-6)
Rearrange equation to slope-intercept form:
y = 1(x-6) + 2
y = x-4
6x=7-4y
Move 'y' to one side
6x-7=-4y
6x-7
------- = y
-4
If you want a answer for this you need to show the graph to us