What is the area of sector CED when DE = 15 yd?
That depends. Is DE the arc length, or the chord length? Then, you have also left out the radius or the subtended angle.
To find the area of a sector, we need two pieces of information: the measure of the central angle of the sector and the radius of the circle. In this case, we know that DE is 15 yards, but we don't have information about the central angle of sector CED or the radius of the circle.
To proceed, we need more information.