Problem Solving

In the figure above, two rectangles with the same dimensions overlap to form the shaded region. If each rectangle has perimeter 12 and the shaded region has perimeter 3, what is the total length of the heavy line segments?
(A) 15 (B) 18 (C) 21
(D) 22 (E) 23

OA is C. Any one can throw some light on how it is the OA?

24(sum of perimeter of 2 rectangle)-3(perimeter of shaded region)=21

sairamGmat wrote:

In the figure above, two rectangles with the same dimensions overlap to form the shaded region. If each rectangle has perimeter 12 and the shaded region has perimeter 3, what is the total length of the heavy line segments?
(A) 15 (B) 18 (C) 21
(D) 22 (E) 23

OA is C. Any one can throw some light on how it is the OA?

What is the source of the question, please? "Heavy line segments" is pretty vague and left to interpretation...