For a structure to be built on a rectangular plot of land with sides of at least 4 meters, a distance of two meters is left from each side of the plot as shown in the figure, and the area shown in gray is determined as the development area and development permission is granted for this area. For this plot with a perimeter of 42 meters, if the determined development area is $24\,\mathrm{m}^2$, what is the length of a diagonal of the determined development area in meters? A) 10 B) 11 C) 12 D) 13 E) 14
For a structure to be built on a rectangular plot of land with sides of at least 4 meters, a distance of two meters is left from each side of the plot as shown in the figure, and the area shown in gray is determined as the development area and development permission is granted for this area.
For this plot with a perimeter of 42 meters, if the determined development area is $24\,\mathrm{m}^2$, what is the length of a diagonal of the determined development area in meters?
A) 10
B) 11
C) 12
D) 13
E) 14