Well if each band needs 15.5 inches and she needs to make 12 headbands she needs 15.5 inches 12 times. Now you can add 15.5 + 15.5 +15.5 (so on) 12 times or you can do it the easier way and do 15.5 times 12. this comes out to 186 inches of ribbon. She estimated 160 inches of ribbon, this is unreasonable because it is significantly less that 186.