Let’s label the part between C and D as X an the part D-B as Y.
Then use the Pythagorean theorem to solve it: A^2 + B^2 = C^2. So C^2 will be b, A^2 will be h and B^2 will be X.
So, 8^2+ x^2 = 16^2, the x is 13.9
The area of the first triangle will be: 13.9*8/2 = 55.6
The D-B line is : 20-13.9= 6.1
The area of the second triangle is : 6.1*8/2 = 24.4
So the A value will be : 24.4 + 55.6 = 80