Answer:
32 shirts
Explanation:
Charges of x shirts by Cool Shirts = 8x + 13
(shipping of shirts = $13)
Charges of x shirts by Total Tees = 7.5x + 16
(Shipping of shirts = $16)
If Cool Shirt offered a deal of free shipping (Shipping = 0),
Charges of x shirts by Cool shirts = 8x
Total charges from both the companies will be equal if,
8x = 7.5x + 16
8x - 7.5x = 16
0.5x = 16
x = 32
Therefore, purchase of 32 shirts will be needed until companies cost the same.