Answer: 19.6ft²
Explanation:
 Formula for finding the area of a circle = πr² where π = 3.142 or 22/7 and 
 r = 5/2 because two radii make one diameter.
 Therefore the area of the circular stained glass = 3.142 x 5/2 x 5/2
 = 3.142 x 25/4
 = 19.638
 ≅ 19.6ft²