16m? = =4m×4m, and the side length of a small square is 4m.
﹙5-4﹚×5÷2+4×4÷2=2.5+8= 10.5m? , the sum of the areas of the two blank triangles above.
﹙5+4﹚×4÷2=9×4÷2= 18m? , the area of the big blank triangle below.
25+ 16- 10.5- 18 = 12.5m? The shadow area is 12.5 square meters.