The distance from AB to CD is 8, and we know that the distance from point D to straight line AB (that is, the height of the base of triangle ADE on AE side) is 8.

The ADE area of the triangle is 1/2×5×8=20.

It is easy to know that F is the midpoint of the BC side, and the distance from F to BE (that is, the height of the base of the triangle BEF on the BE side) is 4.

Then the BEF area of the triangle is 1/2×5×4= 10.

Similarly, the area of triangular DCF is 1/2× 10×4=20.

The total area of parallelogram is 10×8=80, and the triangle area is calculated by subtracting the above three triangle areas.

The answer is: 30