The surface area of a shape is the area of each face added together.
Triangles
The area of a triangle is 1/2*w*h. So 1/2*6*8 = 24. We have two of these faces, so we'll add this twice.
Outer Rectangles
The area of a rectangle is w*h, so for these we'll do 9*20 = 180. These shapes are again duplicates, so we'll add them twice.
Center Rectangle
Again, we know the area of a rectangle is w*h, so 6*20 = 120. This is the only shape that isn't repeated.
Finally, we need to add the areas of the shapes up.
24 + 24 + 180 + 180 + 120 = 528
Therefore the surface area of the net is 528 cm^2.
