All the angles labeled are 90°

The two small portions must be in sum equal to the big one triangle

C is the answer

First recognize that AB is the height of the rectangle ABCD AND AB is the height of triangle AED.

So the area of rectangle ABCD = (AD x AB)
And the area of triangle AED = (1/2)(AD x AB)
In other words, the area of triangle AED is HALF the area of rectangle ABCD
This means the area taken up by triangles ABE and ECD must take up the other HALF of the area of rectangle ABCD.
This means the two quantities are equal.

Answer: C