(9 x 18) + (6 x 2)
(20 x 9) - (3x2)
1) Since in this polygon we can "decompose" into two other polygons we can write the following about the Area:
2) So we can write, since we have two rectangles:
(9 x 18) + (6 x 2) =162+12 = 174
(20 x 9) - (3x2) = 180 -6 = 174
Considering a larger rectangle minus that blue rectangle (3x2).