Angela decided to make a pen for her dog that is 6 feet wide and 9 feet long. However, after looking at the place where she wanted to put the pen, she decided the width should instead measure only 3 feet. If she wants the perimeter of the pen to stay the same, what will be the new length of the pen?
A.
27 feet
B.
24 feet
C.
6 feet
D.
12 feet