If you have an eye for geometry you can see that each shape has the dimensions x by 3x.
Thus, (3 blocks)(3x per block) comes out to 9x=16.2 cm = length of rectangle.
If this is true, then x = 1.8 cm
Then the area of the rect. is (width)(length) = (9 cm)(16.2 cm) = 145.8 cm^2.
Algebraically, 5(1.8 cm)(16.2 cm) = 145.8 cm^2 (answer)