Answer:
A. 320
Step-by-step explanation:
Find the area of the rectangle:
A = length * width = 32 * 20 = 640
Now add two points to the figure, the midpoints of sides CD and ED.
Call the midpoint of CD point G. Call the midpoint of side DE point H.
Notice that the area you want is the area of rectangle ACDE minus the areas of triangles EFD and BDC.
Now look at rectangle FGDE with diagonal FD. The area of rectangle FGDE is half the area of rectangle ACDE, so it's 320. The area of triangle EFD is half the area of rectangle FGDE, so it's 160.
Now we do a similar thing to find the area of triangle BDC. Look at rectangle BCDH with diagonal BD. The are of rectangle BCDH is half of the area of rectangle ACDE, so it's 320. The area of triangle BCD is half the area of rectangle BCDH, so it's 160.
Finally we do the subtraction:
area of ABDF = area of ACDE - area of EFD - area of BDC
area of ABDF = 640 - 320 - 320
area of ABDF = 320
