A construction worker needs to put a rectangular window in the side of a
 building. He knows from measuring that the top and bottom of the window
 have a width of 9 feet and the sides have a length of 12 feet. He also
 measured one diagonal to be 15 feet. What is the length of the other
 diagonal?
 O
 A. 9 feet
 O
 O
 O
 B. 21 feet
 C. 12 feet
 D. 15 feet