Answer: 8 feet.
Explanation:
Given : The students on a decorating committee create a banner.
Let x be the width of the banner.
The length of the banner is 20 feet.
The length of the banner is 2.5 times its width.
Then, we have

Divide both the sides by 2.5 , we get

Therefore, the width (in feet) of the banner= 8 feet.