120 cm²
1) Let's calculate the surface area by calculating each polygon's area. In this polygon we have, considering that this is a building block
2 triangles 4x3

2 triangles = 12 cm²
1 rectangle 6 x 9:

1 rectangle 5 x 9

1 rectangle 3 x 9
![S=3\cdot9=36\operatorname{cm}]()
2) Adding it all up: 12 cm²+54+45+27 = 120 cm²