Tristan has this rectangular bulletin board shown. What is the most she can increase the length of her bulletin board in order to maintain a perimeter of no more than 21 feet?

A. 3ft
B. 3.5ft
C. 6ft
D. 7ft

Tristan has this rectangular bulletin board shown What is the most she can increase the length of her bulletin board in order to maintain a perimeter of no more class=