Answer:
158 cm²
Explanation:
You want the surface area of a rectangular prism whose net is shown.
Area
The surface area of the prism is the area of the net. That area is the sum of the areas of the rectangles that make it up. The rectangles come in pairs that have the same area.
Down the middle we have two pairs of rectangles. One pair is 8 cm wide and 3 cm high; the other is 8 cm wide and 5 cm high. Together the area of those four rectangles is ...
2(8 cm)(3 cm +5 cm) = 2(64 cm²) = 128 cm²
The "wings" of the net are rectangles that are 3 cm by 5 cm, so their total area is ...
2(3 cm)(5 cm) = 30 cm²
The area of the net is then ...
surface area = 128 cm² +30 cm²
surface area = 158 cm²
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Additional comment
If you like, you can use the area formula. It will tell you the same thing for this 3 × 5 × 8 cm prism.
SA = 2(LW +H(L +W)) = 2(3·5) +8(3 +5)) = 2(15 +8·8) = 2(79) = 158 . . . cm²