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:

A) Width = 9/2, length = 10
Rectangle area = length(l)x width(w)
9/2 = 4.5
4.5(l) x 10(w) = 45ft
We do not see a graph above