Answer:
B
Step-by-step explanation:
Flip each 45-45-90 triangle inwards (we can do this because it is a square and squares have all four sides equal). You should get a plain old shaded square, which means that the shaded square is half of the area of the square with side length 16 cm. So, we have (16 cm)^2 or 256 cm^2, which, when halved, is 128 cm^2 or B.
Note: Is it a coincidence that it is half? Does this always happen? ;)
