Have you tried cutting a rectangle to that size and playing with it?
I did that and I did get an answer.
I doubt I did it the best way and my answer could be wrong because my working is on ridiculously scrappy bits of paper.
Thinking about it a little differently.
The area will be the same as the original rectangle minus triangle EFC
If you let FB=y
then you can work out that y=4.2 and FC=5.8
You can work out that the triangle on the top is congruent to the triangle on the bottom
the are of each of thes is 0.5*4*4.2 = 8.4
Add them together and you get 16.8u^2
The area of the original rectangle is 40u^2
If the area of the middle triangle is T
then
40=16.8+2T
T= 11.6u^2
so the area of the pentagon is 16.8+11.6 = 28.4 units squared
or
40-11.6 = 28.4 units square