First, lets divide the polygon into the upper triangle, and the rectangle below
The rectangle is 60 area, as we know, as 5 x 12 is 60.
The triangle area is 6. We know this because the base is 3, 12-9=3, and the height is 4. 9-5=4. Divide that by 2, and you get 6. So the area is 66.