There's a lot of ways to solve this and get the same answer. No matter what, you definitely need to convert feet an yards.
Starting with what you know, one balloon needs 2.5 feet of ribbon.
You also know that three feet make a yard.
Your final answer asks for yards of ribbon for 18 balloons.
So, some ways to solve would be:
1. Multiply 2.5 by 18. That would end up being 45 feet for 18 balloons. You want yards. Yards are bigger than feet, and so you would want to divide. 45 divided by 3 is 15 yards for 18 balloons.
You could also do:
2. Convert first. 2.5 feet would be not a whole number of yards, but you would do 2.5 divided by 3. It would be a decimal ( you could find out in a calculator ) then, multiply by 18 for the number of balloons and you get 15 yards for 18 balloons.
