You have 10 rolls and each is 6 feet so therefore you have 60 feet of ribbon. Convert that to inches you need to multiply by 12 so 60 x 12 = 720 inches of ribbon.
If the dress maker needs 18 inch pieces you divide to 720 by 18.
720 divided by 18 will give you 40 pieces.
Final answer:
The dressmaker will get 40, 18-inch pieces of ribbon from 10, 6 foot rolls.