Hi there!
To find the surface area, we need to find the area of all of the faces. The triangle face = 4 x 6, and the rectangular faces = 2(5 x 12) + 1(6 x 12). All we are doing is simply finding the area of each face and adding it together. The area of the triangles = 24, and the area of the rectangles = 192. Then, add the two values to get 216cm^2.
Hope this helps!! :)
If there's anything else that I can help you with, please let me know!
