Answer: 21 feet rope costs $28.35
Explanation:
First, we have to see how much 1 foot rope costs. To do this, we have to do 20.25 / 15
20.25 / 15 = 1.35
Now that we know how much 1 foot costs, now we have to see how much 21 feet costs by doing
1.35 x 21
1.35 x 21 = 28.35
So, 21 feet rope costs $28.35