In the diagram, \triangle A B C is a right-angled isosceles triangle. D is the midpoint of B C and E is the midpoint of A B. If A B=B C=24 \mathrm{~cm}, what is the area of \triangle A E D?
Answer Choices
A. 48 \mathrm{~cm}^{2}
B. 36 \mathrm{~cm}^{2}
C. 72 \mathrm{~cm}^{2}
D. 9 \mathrm{~cm}^{2}
E. 54 \mathrm{~cm}^{2}