The area of a triangle is (1/2)bh. But we don't know the base or height of triangle BCD. Is there a way to find them? Always take note of any shapes in a picture, especially the shapes that aren't mentioned. Notice that there is another triangle with the same base and height as triangle BCD, i.e. triangle ADC. Since it has the same base and same height, it must have the same area. And since triangle ADC is simply triangles ADE and CDE stuck together, we can add their areas to get the answer. Since 16 + 12 is 28, D is the answer.