Answer:
7 t-shirts
Step-by-step explanation:
Because you know the cost of shipping ($6) is constant no matter the quantity you order (fixed cost), you can subtract it from the total cost of the order to find the total variable cost. Next you divide the left over cost by the cost per t-shirt to get the quantity ordered.
$111 - 6 = $105
$105 / $15 per shirt = 7 t-shirts
Hope this helps!
-The Business Man