Solution :
Given that , Ribbon candy costs 2.50 per foot.
To calculate the length of Ribbon candy you can buy with 11.25, first you need to calculate the length of Ribbon candy you can buy with 1.
Solving it by Unitary Method,
In 2.50 you can buy 1 foot Ribbon candy,
In 1 you can buy
foot Ribbon candy,
So, In 11.25 you can buy 
Hece , In 11.25 you can buy 4,5 foot of ribbon candy.