Let's break it down, this is easy.
If she needs 2.5 feet of ribbon for every balloon and there are 18 balloons, that would be 2.5 X 18
half of 18 is 9
18+18=36
36+9=45
She would need 45 feet of ribbon, to convert that to yards just divide by 3
45/3=15
she needs 15 yards of ribbon for all 18 balloons
