In the diagram, ABCDEFG is a room having square corners, with EF=20\:m,AB=10\:m, and AG=GF. The total area of the room is 280\:m^2. A wall is built from A to D creating two rooms of equal area. What is the distance, in metres, from C to D?
Answer Choices
A. 15
B. \frac{50}{3}
C. 12
D. 13
E. \frac{40}{3}