imagine the rectangle around the original shape, it would be LxW which wold be 9 x 6 = 54. Then if you find the area of the two triangles cut out of the left and right sides, each triangle area is 1/2 base x height, which is 1/2(6x2)=1/2(12)=6 and x2 for 2 triangles and that = 12.
