The area of the polygon is the sum of the areas of the triangle and the rectangle it sits on. The dimensions of the triangle can be found by examining the top/bottom dimensions shown and the left/right dimensions shown.
The width (base) of the triangle is the difference between the lengths of the bottom and top horizontal lines: (12 -9) cm = 3 cm.
The height of the triangle is the difference between the lengths of the left and right sides of the figure: (9 -5) cm = 4 cm.
The dimensions of the rectangle are shown a the bottom and the left sides of the figure.
